Physics B‑class Mid‑importance

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• Any exposure to around 100 g or more, even if momentary, is likely to be lethal.

• Formula One race car driver David Purley survived an estimated 179.8 g in 1977 when he decelerated from 172 km·h−1 (107 mph) to 0 in a distance of 66 cm (26 inches) after his throttle got stuck wide open and he hit a wall.

--

Not necessarily: The first means "Don't try this at home", the second means "but you might get lucky" (roughly). I'd imagine that repeating the experiment is unlikely to be healthy. It is conceivable that restraints reduced the g force somewhat or otherwise made it more likely than usual to be safe. Ealex292 03:56, 1 December 2006 (UTC)[reply]

74.129.197.37 (talk)

There are so many factors as to make it nearly impossible to determine the g-force a particular person can survive. Think of the 100g's as an 'LD50' - that is, at least 50% of people would die after being exposed to greater than 100g's. —Preceding unsigned comment added by 74.129.197.37 (talk) 05:59, 15 December 2007 (UTC)[reply]

People looking for the graphics card GeForce may end up on this page, as gforce redirects here. Just a note JayKeaton 15:01, 29 November 2006 (UTC)[reply]

The article claims that the variations in the acceleration due to the gravity of the earth are due to so-called centrifugal forces. This is a poor explanation. I believe a better one would be:

One reason involves the difference in the distance from the centre of the Earth between the two positions due to the equatorial bulge – this leads to a variation in the gravitational field strength. The equator is further away from the centre of the Earth than the poles leading to a difference of about 0.05 m s–2. The second reason is due to the rotation of the Earth. The person on the equator experiences a centripetal acceleration. Given that the scales read the normal (or reaction) force N, in this case N = m(g–ac). Therefore there is a slight reduction (of the order of the first effect) —Preceding unsigned comment added by 132.181.7.1 (talk • contribs)

The article states in the introduction

g-force or g-load is a force-equivalent, equal to 9.80665 N/kg

but N/kg is a unit of acceleration, not of force, so I have to conclude that 1 g = 1 g-force. Is that intended? AxelBoldt 18:09, 19 December 2006 (UTC)[reply]

Shouldn't this article include the difference of g force divided by time?

There are great difference of experiencing 10 g's for a millisecond and for ten seconds. A person have experienced and survived over 46 g's in a certain amount of time, but it is lethal to experience for example 25 g's over a minute. This difference may not be understandable in this article.

It might be helpful to note that the version of Helmert's equation in the article is equivalent to the following (discounting rounding errors and expression of lengths in cm instead of meters):

http://lists.nau.edu/cgi-bin/wa?A2=ind0101&L=phys-l&P=39244

g = 980.616 - 2.5928*cos(2*phi) + 0.0069*cos^2(2*phi) - 3.086x10^(-6)*H

where: phi = latitude H = elevation (in cm)

This version is on several web pages and in a CRC Chemistry and Physics Handbook, where it can be difficult to find as noted here:

http://www.lhup.edu/~dsimanek/scenario/labman1/accel!.htm In a CRC handbook like mine, there's no index entry for Helmert's equation. Look up "acceleration due to gravity at any latitude and elevation, equation." It is in the "definitions and formulas" section.

The version above may be calculated more quickly because only one trig value is needed: cos(2*phi). Once that trig value is known, it can be squared for the third term. The version in the article requires calculating two trig values separately: sin(phi) and sin(2*phi).

It may be of interest that there is another, equivalent, version of this formula (with no double-angle trig arguments) which may be obtained by applying trig identities in yet another way. It has the form: g = g_0 * (1 + a * (sin(phi))^2 + b * (sin(phi))^4)

This latter version is not found as frequently on the web, but it is here: http://galitzin.mines.edu/INTROGP/notes_template.jsp?url=GRAV%2FNOTES%2Flcorrect.html&page=Gravity%3A%20Notes%3A%20Latitude%20Variation%20Corrections Ac44ck 07:33, 28 January 2007 (UTC)[reply]

There seems to be a more recent (1984) formula for the variation in g with latitude: http://earth-info.nga.mil/GandG/publications/tr8350.2/tr8350.2-a/Chapter%204.pdf

g = 9.7803267714 * (1 + 0.00193185138639 * (sin(L))^2) / sqrt(1 - 0.00669437999013 * (sin(L))^2)

This formula is on page 3 of the pdf file.

Ac44ck 07:38, 28 January 2007 (UTC)[reply]

Probably there's someone with higher g-force survived http://en.wikipedia.org/wiki/Kenny_Brack#Return_to_IRL --84.234.42.68 21:33, 20 June 2007 (UTC)[reply]

I wondered about the paragraph on amusement rides, where it is said that they usually don't pull over 3 g with some listed exceptions. However, according to "rcdb.com" and other coaster-related sources, almost every looping coaster on the world pulls about 4-5 g on entering the loop (e.g. the Vekoma Boomerang which is found in many parks around the world is said to pull 5.2 g on its first inversion).—Preceding unsigned comment added by 141.203.254.65 (talk • contribs)

To me, the first couple of sections are a bit confusing. I was going to tweak a few things, but in fact ended up effectively rewriting the intro and "Explanation" sections, and incorporating the "Convenient definition" section. Because it's a relatively significant change I feel I should give others the opportunity to comment before applying it to the article. This is what I've got. Matt 02:53, 25 July 2007 (UTC).

g-force (also gee-force, gee-loading) is a measurement of an object's acceleration expressed in gees. The "gee" (pronounced [dʒiː]; symbol g) is a non-SI unit equal to the nominal acceleration due to gravity on Earth at sea level, defined as 9.80665 m/s², or approximately 32.174 ft/s². More precisely, g-force measures the difference between the acceleration that an object actually experiences and the acceleration that gravity is trying to impart to it, as explained further below. The symbol g is properly written in lowercase and italic, to distinguish it from the symbol G, the gravitational constant, which is always written in uppercase; and from g, the symbol for gram, which is not italicized.

Although strictly a measurement of acceleration, the term g-force, as its name implies, is commonly understood to refer to the force that an accelerating object "feels", expressed as a multiple of the force that it "feels" when resting stationary on the Earth's surface. The relationship between force and acceleration stems from Newton's second law, F = ma, where F is force, m is mass and a is acceleration.

These so-called "g-forces" are experienced, for example, by fighter jet pilots or riders on a roller coaster, and are caused by changes in speed and direction. For example, on a roller coaster high positive g-forces are experienced on the car's path up the hills, where riders feel as if they weigh more than usual. This is reversed on the car's descent where lower g-forces occur, causing the riders to feel lighter or even weightless.

Because of the potential for confusion about whether g-force measures acceleration or force, the term is considered by some to be a misnomer. Scientific usage prefers explicit reference to either acceleration or force, and use of the appropriate units (in the SI system, metres per second per second for acceleration, and newtons for force).

Calculating g-forces [level 2 heading]

Unlike simple acceleration, g-force is a measure of an object's acceleration relative to the local gravitational acceleration vector, rather than being compared to an inertial reference frame. In other words, it is the (vector) difference between an object's actual acceleration and the acceleration that it would experience if it were falling freely. It is this difference, rather than the actual acceleration of the object, that gives rise to the feeling of force ("apparent weight"), and hence to the feeling of heaviness and lightness in high and low g-force environments. For further details, including examples of conversion between acceleration and apparent weight force, see apparent weight.

In a simplified scenario, where accelerations are assumed to act only downwards (positive) or upwards (negative), calculating this difference simply amounts to subtracting the object's actual acceleration from the gravitational acceleration. For an object on or near the Earth's surface, gravitational acceleration is for practical purposes equal to 1 g. (For more precise measurements, the variation of Earth's gravity with location and altitude must be taken into account.) So, for example:

• A non-accelerating object experiences a g-force of 1g − 0g, or just 1g ("normal weight").

• An object in free fall (accelerating downards at 1g) experiences a g-force of 1g − 1g = 0g ("weightless")

• An object accelerating upwards at 1g experiences a g-force of 1g − (−1g) = 2g ("twice normal weight")

• An object accelerating downwards at 2g experiences a g-force of 1g − 2g = −1g ("negative g").

More generally, the object's acceleraion may act in any direction (not just vertically), so in a fuller treatement it must be considered as a vector quantity. The "difference" in acceleration that g-force measures is found by vector addition of the opposite of the actual acceleration and the local gravitational acceleration vector (about 1 g downward on or near the Earth's surface).

In cases when the magnitude of the acceleration is relatively large compared to 1 g, and/or is more-or-less horizontal, the effect of the Earth's gravity is sometimes ignored in everyday treatments. For example, if a person in an car accident decelerates from 30 m/s to rest in 0.2 seconds, then its deceleration is 150 m/s², so one might say that it experiences a g-force of about 150/9.8 g, or about 15.3 g. Strictly speaking, due to the vector addition of the gravitational acceleration, the true g-force has a slightly larger magnitude and is pointing slightly downwards (intuitively this is because the car is already experiencing 1 g just by sitting on the road).

Comments on proposed changes

• I don't think example calculations should be included. Explained some but no great detail. It looks like a tutorial thing to me. What about the human tolerance & experience stuff? Do you want to get rid of that? I wouldn't mind that, at least cut it back. -Fnlayson 14:01, 25 July 2007 (UTC)[reply]

• • Sorry, perhaps it wasn't clear. This is a replacement just for the current intro, "Explanation" and "Convenient Definition" sections - the first part of the article. I wasn't proposing at this stage making any changes to the rest of the article. I think that the examples are important, but I take your point that it seems a little too detailed. I have amended the above to cut down on the detail. Matt 13:08, 26 July 2007 (UTC).

• I've now replaced with the above, overwriting a recent change claiming:

g-force (also gee-force, gee-loading) is a non-SI vector measure of force, where 1 g (pronounced [dʒiː]) is defined to be the force an object would experience by gravity at the surface of the earth (the units are newtons or pound-force).

This is wrong. The "gee" (symbol g) is a unit of acceleration, not force. In any case a unit can't be defined as the force "an object" would experience -- it depends on the object. Matt 12:39, 28 July 2007 (UTC).

Agreed. 1 g is the acceleration an object experiences on the Earth's surface. -Fnlayson 16:12, 28 July 2007 (UTC)[reply]

If we are talking about g-force, then it is a force. It is described by the acceleration which causes that force. Lets try to get this right. Rlsheehan August 12, 2007

• Resulting force has nothing to do with it. That's a reaction force, internal force. G-force is an acceleration divided by acceleration of gravity so it is in g's. Having force in the name does not mean anything, since its units are g's not force units. -Fnlayson 03:17, 13 August 2007 (UTC)[reply]
• I agree that "g-force" is a misnomer. Using this name confuses many people about force vs acceleration. If we call it a force, then it should be a force. It can still be described by the accleration which causes it. Rlsheehan Aug 14, 07
  • G-force is simply described as an acceleration in g's now. What do you suggest? -Fnlayson 15:17, 13 August 2007 (UTC)[reply]

*It is certainly acceptable to report accelerations in the non-SI unit of g-s: see also Shock (mechanics). The confusion is that we are trying to call this a force. Perhaps a new first paragraph like this might help:

"g-force is a comomonly used term which can have two different but related meanings: 1) the acceleration on an object or person expressed in gs and 2) the reaction force resulting from an applied acceleration, expressed in gs." Rlsheehan Aug 13, 07

I've removed statement 2 since a force cannot be "expressed in g's" — any more than velocity can be expressed in kilograms, or time expressed in litres. The g is a unit of acceleration and that's that. Force per unit mass could be expressed in g's though. I think I mentioned that in the article at one point, but it got taken out for some reason. Matt 00:09, 30 August 2007 (UTC). —Preceding unsigned comment added by 86.134.55.114 (talk)

The item we are discussing is g-force, thus we must include the force interprretation. Yes, the term is probably a misnomer, but ,it is here and we can discuss it. It can be a force described by the acceleration which causes it: the causing acceleration can be described in terms of gs. Rlsheehan 01:56, 5 September 2007 (UTC)[reply]

• Yea and that is explained in the "Connection with force" section. No need for that to be in the Lead too. -Fnlayson 02:43, 5 September 2007 (UTC)[reply]

Yes, it is important to start with a correct lead paragraph. The subject is g-force so force must be included in the lead paragraph. Otherwise, change the title. Rlsheehan 14:12, 5 September 2007 (UTC)[reply]

in the 'human g-forces' section it says "a weight of 1g" a few times.

g is in N/kg and a weight is in kg, so this seems incorrect to me.

Any suggestions?

Mushlack 20:00, 4 August 2007 (UTC)[reply]

• Weight is a force by scientific and tehnical definations. The SI unit for force is Newton (N) and the SI unit for mass is kilogram (kg). But the acceleration of gravity is not a weight either. So the wording should be adjusted/corrected. -Fnlayson 20:39, 4 August 2007 (UTC)[reply]

Is the g in this article really properly italicized? Robert K S 07:42, 21 September 2007 (UTC)[reply]

• I had the same thought, assuming you're talking about the "g" in "g-force" (rather than the standalone unit symbol). I have not found any dictionary that italicises the g, and unless anyone can provide some authority that says it should be italicised I propose the italics should be removed throughout. Matt 00:43, 23 October 2007 (UTC). —Preceding unsigned comment added by 86.136.195.74 (talk)

• • I've also looked at a selection of pages thrown up by Google, and basically I can't find anyone who italicises the "g" in g-force, so I've removed it. If you disagree and think it should be italicised then we need a solid authority I think... Matt 02:05, 31 October 2007 (UTC). —Preceding unsigned comment added by 86.150.100.198 (talk)

Just a quick point: in the part about human tolerances, various references are made to difference tolerances with "eyeballs-in" or "eyeballs-out". Perhaps there should be an explanation of the term? I'd put it in if I knew what it meant myself, but I really don't... anyone else have a clue? Is it about eyes being open or closed? Eyes being slightly popped out of their sockets? Thanks. Hagger 19:09, 17 October 2007 (UTC)[reply]

Yeah, an eyeballs-out g-force 'tries' to pop the eyes out, an eyeballs-in g-force 'tries' push them in. It must be emphasised that it doesn't succeed in either case in any survivable situation ;-)- (User) WolfKeeper (Talk) 01:04, 17 December 2007 (UTC)[reply]

I'm skeptical about the Formula One data must be wrong. On a level road, with no airfoil, the greatest acceleration a car can have is mu*g, where mu is the coefficient of static friction, and g is the acceleration of gravity. Since mu for rubber on asphalt is no more than about 0.5, the greatest acceleration or deceleration you can have is about 0.5 gees. Unless these figures are referring to banked turns, or the cars have airfoils that can generate a downward force equal to 10 times the cars' weight, I don't think the article can be correct. Is there a source for these numbers?--76.81.160.198 (talk) 03:44, 10 December 2007 (UTC)[reply]

Your figures are way off. Standard cars can pull about .92 g on a dry road. Motorbikes with relatively sticky tires can pull over 1.2 g. Formula one cars have sticky tyres and downforce at maximum speed of about 5 or 6 times their own weight or more due to groundforce (predominately), but also the wings help some as well.- (User) WolfKeeper (Talk) 04:16, 10 December 2007 (UTC)[reply]

Oh yeah, and formula 1 cars go fast enough that just lifting off at high speeds gives about 1g deceleration (with the 'help' of the rear wing); putting the brakes on as well adds another 4g or so, even though they have relatively small front tyres.- (User) WolfKeeper (Talk) 04:20, 10 December 2007 (UTC)[reply]

Okay, if the airfoils really do produce a force many times greater than gravity, then the figures in the article are plausible.--76.81.160.198 (talk) 22:03, 16 December 2007 (UTC)[reply]

Oh yeah, massive downforce. Somebody calculated that a formula one car could theoretically drive continuously upside down from about 100 mph, but fortunately (or unfortunately), there's no upside down tracks anywhere to try this ;-)- (User) WolfKeeper (Talk) 01:01, 17 December 2007 (UTC)[reply]

I noticed that there is citation for the g-forces that Formula One drivers usually experience. I think that the figures are okay but they should be verified by a reliable source. --Cryonic07 ^talk ° ^contribs 21:36, 9 June 2008 (UTC)[reply]

So... a punch or a kick to an applied area can actually reach beyond 5 or 9 g, relative to a cough or sneeze?

88.105.47.71 (talk) 22:54, 14 September 2008 (UTC)[reply]

Yes, but these are usually under the category of Shock (mechanics). Rlsheehan (talk) 16:19, 15 September 2008 (UTC)[reply]

It appears that some Web sites might be saying g is italicized because they are now parroting Wikipedia. Granted it might be a *splendid* idea to not have the g for acceleration be the exact same symbol as that for the SI unit gram, but to just flat state that the g (acceleration) is italicized must be properly cited. For on thing, italicizing a unit symbol is a colossal violation of an even more important principle that only variables are italicized; unit symbols are always roman (according to the SI Brochure section 5.1). Note too, this NASA page and this medical site. Note too this account of Colonel Stapp, the rocket-sled guy. Or Splung.com/Physcis. All use roman g. I’ve never seen an italic g in aerospace publications. This included Aviation Week & Space Technology, a magazine I subscribe to and which is the preeminent, authoritative trade publication. As for confusion with the gram, note as you read through these articles, no one with any common sense is for a moment confused and thinks that Stapp was exposed to “40 grams.” Besides, regardless of whether or not g ought to be italicized, it is not the job of Wikipedia to advocate change by suggesting in a factual way that “this is the way it’s done” if it is actually not done that way in the real world.

It seems to me that if we are going to cite some source that effectively says that NASA is doing it all wrong, whomever it is we’re citing oughta have some serious credentials. Greg L (talk) 05:42, 13 January 2009 (UTC)[reply]

I think that those writing 5 g simply mean five times the variable g (i.e. the magnitude of the local gravitational field), and in many cases the difference between it and the defined value 9.806 65 m/s² is irrelevant. (You still italicize the speed of light c, even if you are using it in a way typical of units of measurement.) But I agree that I would not italicize g if I meant the unit of measurement equal to 9.806 65 m/s² exactly, by definition regardless of local gravity. -- Army1987 – Deeds, not words. 13:24, 13 January 2009 (UTC)[reply]

Clearly not Army. The article appears to have been written by someone who tried to Change the World to Be a Better and Brighter Place™©®. This article states as follows:

The g (Template:PronEng) is a non-SI unit equal to the nominal acceleration of gravity on Earth at sea level (standard gravity), which is defined as 9.80665 m/s² (32.174 ft/s²). The symbol g is properly written both lowercase and italic^{[citation needed]} to distinguish it from the symbol G, the gravitational constant and g, the symbol for gram, a unit of mass, which is not italicized.

I put the {cite} tag there, otherwise, it would have appeared to be uncontested, authoritative fact.

And this quotation from this article:

Thus, in a simplified scenario where accelerations are assumed to act only upwards (positive) or downwards (negative), calculating g-force simply amounts to subtracting the acceleration (relative to the Earth) due to Earth's gravity (1 g in the downwards direction) from the object's acceleration relative to Earth. Since we are taking downward acceleration as negative, this is equivalent to adding 1 g. So, for example:

• An object at rest with respect to the Earth experiences a g-force of 0 g + 1 g, or just 1 g ("normal weight").

• An object in free fall (accelerating downwards at 1 g relative to the Earth) experiences a g-force of −1 g + 1 g = 0 g ("weightless")

• An object accelerating upwards at 1 g relative to the Earth experiences a g-force of 1 g + 1 g = 2 g ("twice normal weight")

• An object accelerating downwards at 2 g relative to the Earth experiences a g-force of −2 g + 1 g = −1 g ("negative g").

It also appears to me to be misinformation propagates to articles that link here. For instance, look at the second paragraph of Sprint (missile). It says The Sprint accelerated at 100 g, reaching a speed of Mach 10 in 5 seconds. The same thing occurred on our Shockwave (Drayton Manor Theme Park) roller coaster article: italicized g.

It is extremely hard to prove a negative (prove that just because I can’t find an authoritative source saying that g is italicized, that one doesn’t exist). However, the only “sources” I can find seem to be amateurish, tertiary ones that—unfortunately—took their guidance from here. The long-standing rule that units are roman and variables are italicized underlies why real-world usage by NASA and industry use “g”. Industry doesn’t seem to have followed Wikipedia’s lead into a Better and Brighter Future. Check out the spec page for this accelerometer or this one by Honeywell. They all use “g”.

It appears that article used italic g from the very beginning as some sort of house style to avoid confusion with the gram. Unfortunately, we can’t do that. If one examines any other encyclopedia, one will see that they don’t perceive a need to try to change the world because the same unit symbol means two different thing across their publications. Examine this first edit by Wolfkeeper. It could also be that he simply copy/pasted an article from elsewhere and didn’t advance such a notion himself. I’ve alerted him on his talk page.

I’ll give a full 24 hours for someone to cite this (or make a valiant effort to defend it because “it oughta be that way”), and then I will see if some bot operators can help correct all the articles that link here—there are about a thousand of them. Greg L (talk) 17:35, 13 January 2009 (UTC)[reply]

I think the general rule is that where a quantity symbol (such as g for gravity or m for mass) might conflict with a unit of measurement symbol (such as g for gram or m for metre), you should italicize the quantity symbol and leave the unit of measure symbol in roman type. My source for this is the Canadian government style manual (The Canadian Style, Dundham Press in co-operation with Public Works and Government Services Canada). Since NASA is in the US, and the US is somewhat out of step with the rest of the world as regards units of measure, this issue may not arise as often for them as it would for organizations in other countries, where the gram is the standard unit of mass. Note that g for gravity is not really a unit of measure, it's really a constant, equal to the average rate of gravitational acceleration on this particular planet (9.8 m/s²).RockyMtnGuy (talk) 17:01, 13 January 2009 (UTC)[reply]

• RockyMtnGuy. First the facts. The article (incorrectly as far as I can see) states as follows:

The g (Template:PronEng) is a non-SI unit equal to the nominal acceleration of gravity on Earth at sea level (standard gravity), which is defined as 9.80665 m/s² (32.174 ft/s²). The symbol g is properly written both lowercase and italic^{[citation needed]} to distinguish it from the symbol G, the gravitational constant and g, the symbol for gram, a unit of mass, which is not italicized.

The g is clearly a unit of measure and it is used that way in the real world. 100 g by definition is 980.665 m/s². For a 0.1% accuracy transducer, 100 g is 981 m/s². That’s what the unit means. The article further clearly states that the unit symbol (representing the value of acceleration) is italicized. This flouts the rule observed in all good science that unit symbols are always roman text and variables are always italicized (SI Brochure section 5.1). Further, it flouts all real-world practice by any scientist or academic or engineer experienced in the art of acceleration.

As regards g as a variable, if one is writing a formula where acceleration is a variable, one customarily uses a, as in F = ma. I’m sorry, but it is not passing my “grin test” here that F = mg is a common way of doing it, nor that NASA is out in left field here.

An important point is it is not Wikipedia policy to use the Canadian Manual of Style; we follow broadly accepted, internationally recognized, real-world practices. Secondly, you are misinterpreting what the Canadian government style manual is saying. They don’t mean confusion arrises if g (acceleration) and g (gram) are “in the same encyclopedia”, they mean precisely what they said: “where a quantity symbol (such as g for gravity or m for mass) might conflict with a unit of measurement symbol (such as g for gram”).

This potential for real-world confusion doesn’t happen too often, where one must discuss grams and gees in the same article. For instance, this account of Colonel Stapp, the rocket-sled guy is rather common. So too is this NASA page. Both speak to the issue of accelerations and don’t make mention of the gram; ergo, there no conflict where confusion might arise. It is even less often that one mentions grams and gees so often in the same article that one needs to use unit symbols “g” for both. Nevertheless, the requirement to discuss mass and g's in the same document does happen if you are a manufacturer of accelerometers and they need to provide technical specs of the transducers themselves. The practical way to avoid the confusion is just use kg for mass, as is done in the real world by Honeywell with their accelerometers (data sheet). In that data sheet (obviously written for a European audience), they write Weight, AG111: 0,03 kg [1 oz]. An even better way, IMO, would be to simply write out the unit name: Transducer weight: 30 grams or Transducer weight: 0.03 kilogram since this pulls the rug out from under any arguments that writing “kg” might lead someone to think that weight is being measured in kilogees (although that doesn’t pass any realistic “grin test” either).

As I wrote above, the vast, vast majority of authoritative organizations and companies such as NASA and the manufacturers of instruments that measure g-force use the unit symbol as all unit symbols must be: roman (upright) text. We must follow real-world practices here and certainly must not flout fundamental practices observed in all proper mathematics and science. We should also avoid the misperception that just because there is technically a potential for confusion, that there is a genuine real-world problem. Examine, for instance, this hypothetical: The lake in 1999 measured only 2.6×10¹³ litres but we measured 2 gal notwithstanding its lack of volume. The world doesn’t need us POV-pushing and inventing house styles based on perceived shortcomings with the way the world really works. Greg L (talk) 18:04, 13 January 2009 (UTC)[reply]

I'm not quite sure who is POV pushing. We have a reliable source that says that having g in italic form is valid.- (User) Wolfkeeper (Talk) 22:58, 13 January 2009 (UTC)[reply]

• I assume you are referring to the Canadian Manual of Style? That is not what they said. “Valid” only in under very special circumstances. What they said (and mean) is that if you have a document where the symbol g for gram is simultaneously being used with the gee, to put the gee in italics. Short of this, the unit symbol for gee (g) follows the convention universally used for unit symbols and as it is used by the rest of the world. What is clear is that you don’t always (in fact, quite rarely) make the unit symbol italic. Further, there are infinitely more superior ways to avoid such confusion; just write out he word gram. If someone wants to put that Canadian bit of advise (regarding articles where there is potential for conflict) into our article, that’s fine with me, but it needs to be properly and fully cited.

  I applaud your desire to banish all potential for confusion from the halls of Wikipedia. But the onus really needs to be centered squarely upon the facts and standard practices. How many manufacturers of accelerometers can you find that use g in italics? I’ve cited two, above, that use it in roman. Or do you think they—like NASA—are simply all wrong here? Greg L (talk) 23:13, 13 January 2009 (UTC)[reply]

Quite frankly, you just seem to be trying to force a US convention on the entire wikipedia, this all seems very WP:POINTy to me. NASA is a US-government organisation that historically has exclusively used imperial units (but is moving to almost exclusively use SI now), and hence historically would have seen absolutely no reason to use the italic form. All of the other manufacturers you quoted were American. The wikipedia by and large (but not exclusively) leans towards SI units, and this generally encourages the use of g rather than g.- (User) Wolfkeeper (Talk) 00:13, 14 January 2009 (UTC)[reply]

FWIW I just checked 'Rocket Propulsion Elements' (7th edition) by Sutton, which is about as near to being a standard rocket handbook as you can get (and he's an American author), and on page 214 he refers to zero-g. I just don't think that your suggestion that the entire wikipedia be changed is going to fly with notable examples like that. I'm also finding that g0 in general on the web, is nearly always written in italics where this is possible; and again Sutton uses this throughout.- (User) Wolfkeeper (Talk) 00:13, 14 January 2009 (UTC)[reply]

• We seem to be short on facts—at least the kind you like. Please produce verifiable sources saying that g is generally supposed to be italic. Please cite the Canadian Manual of Style, in full. If it is a Web address, please provide that. If it is a book, please cite the ISBN and provide the full wording of what it says on the subject. Let’s get that much out of the way.

  As for your dismissing my links (NASA and two manufacturers of accelerometers) as being “American”, let’s examine the very first two Web sites I’ve come across for foreign suppliers of accelerometers: Active Robots in the UK, and Farnell in Australia. They are, not surprisingly to me, using roman g.

  Further, I utterly reject your method of “proving” anything by (supposedly) citing a book of yours that uses an italic g. That isn’t verifiable, and is also anecdotal. The question is, what is the world-wide standard. And if the US style is different from the world-wide standard, then our article needs to state as much. Please demonstrate what you suggest: that world-wide practice outside of the U.S. is italic. The very first two sources say this is not so. I note also, curiously, that you dismissed my manufacturers as being American (suggesting that the world-wide practice is italic) and then didn’t provide any Euro manufacturers or distributors of accelerometers yourself. Greg L (talk) 00:58, 14 January 2009 (UTC)[reply]

I don't think you understand. Sutton is the rocket text book. He's probably more authoritative than NASA by and large. And the 7th edition was the one that converted to SI.googlebooks Look, I'm not going to argue this any longer, this is a waste of time, I've made slight changes to the article. Any attempt to systematically remove italic use from the wikipedia is going to be reverted as being undue weight and failing to represent a global point of view. I agree that non italic 'g' is used in some cases, particularly in America, and maybe in some or all accelerometer manufacturers literature (particularly if they want to sell into the American market I imagine), but that's not enough.- (User) Wolfkeeper (Talk) 01:23, 14 January 2009 (UTC)[reply]

• You seem to be short on verifiable facts—at least the kind of facts that you are founding a shaky premiss upon. A book proves absolutely nothing. Please produce verifiable sources from an internationally recognized standards body saying that g is *generally* supposed to be italic. Please cite the Canadian Manual of Style, in full. From RockyMtnGuy’s description, it sounds like this is not what they are saying. If it is a Web address, please provide that. If it is a book, please cite the ISBN and provide the full wording of what it says on the subject. Let’s get that much out of the way.

  As for your dismissing my links (NASA and two manufacturers of accelerometers) as being “American”, let’s examine the very first two Web sites I’ve come across for foreign suppliers of accelerometers: Active Robots in the UK, and Farnell in Australia. They are, not surprisingly to me, using roman g. As for NASA being American (and how their practices are at odds with the rest of the world), check out ESA’s GOCE Web site. I’m sorry, but the World-Wide practice by WP:reliable sources is clearly roman.

  Finally, your statement The wikipedia by and large (but not exclusively) leans towards SI units, and this generally encourages the use of g rather than g is a non sequitur; yes, Wikipedia tends towards SI, but that doesn’t in the least prove that the world flouts a world-wide standard that unit symbols are always roman—italic is reserved strictly for variables. In fact, it demonstrates the opposite, since the rule of the SI is clear on this subject: Unit symbols are printed in roman (upright) type regardless of the type used in the surrounding text. This is in keeping with the long-standing practice in mathematics and engineering since the at least the time of Newton.

  Finally, please don’t threaten to editwar over this (Any attempt to systematically remove italic use from the wikipedia is going to be reverted as being undue weight and failing to represent a global point of view.). The only way to win here is to prove that the world-wide practice is italic and I’ve just demonstrated that the most reliable sources—world wide—is clearly roman. American manufacturers of accelerometers for measuring g-force, world-wide distributors of accelerometers, American space agency, European space agency. Simply threatening to editwar and revert doesn’t cut it. Give it up please; it’s a lost cause. Greg L (talk) 01:29, 14 January 2009 (UTC)[reply]

Greg, "only variables are italicized"? But then why do our articles on e (elementary charge) and e (mathematical constant) italicize e? Are they both wrong?--Goodmorningworld (talk) 05:10, 14 January 2009 (UTC)[reply]

I'd also like him to explain why he thinks a reference to a documents about SI units is binding on g when g isn't even an SI unit and so is outside the scope of the documnent! In other words he has only American references and a couple of advertising specifications by some companies trying to sell stuff on a web page. These weren't even PDF files or anything. This is all incredibly tendentious.- (User) Wolfkeeper (Talk) 12:57, 14 January 2009 (UTC)[reply]

This whole discussion is too weird for words. The whole point of using italics is to avoid confusing symbols for quantities (such as gravity) with symbols for units (such as gram). However, after a little Googling, I found that the final authority on the subject is the International Bureau of Weights and Measures (BIPM) and the issue was decided by the Conférence Générale des Poids et Mesures (CGPM) in 1901, where they decided that the standard acceleration due to gravity was g_n = 9.80665 m/s². See: Declaration on the unit of mass and on the definition of weight; conventional value of gn. The US National Institute of Science and Technology (NIST) followed their lead. Note that the symbol used was "g_n". Italicized "g", subscript roman "n". Other symbols are often used, such as "g", "g","g₀", "G", and "gee", but they aren't really internationally recognized.RockyMtnGuy (talk) 05:28, 14 January 2009 (UTC)[reply]

• This is quite surreal for me too. Although BIMP may be the world authority, I don't think this is the relevant document. While it uses italicized "g", subscript roman "n", the footnote to the resolution states the italicised gn notation to be obsolete. Nowhere does this state categorically, infer or imply that gee is to be denoted by g, if you see what I mean. Ohconfucius (talk) 07:34, 14 January 2009 (UTC)[reply]

I just checked that, and I don't see anything that declares gn to be obsolete. They simply declare what the acceleration due to gravity is, but unfortunately fail to give it a symbol to denote it.- (User) Wolfkeeper (Talk) 14:00, 14 January 2009 (UTC)[reply]

I'm sorry, but it quite rightly says that kilogram force (kgf) is obsolete, not g or gn; you misread it.- (User) Wolfkeeper (Talk) 14:19, 14 January 2009 (UTC)[reply]

• Yes. You are quite right Wolfkeeper. In 1901, before the Wright brothers first flew, the BIPM referred to one Earth gravity as g_n. Are you suggesting that this, somehow, is relevant other than as a historical footnote about yet another BIPM proposal that was trampled into the dust by the real world? The BIPM currently says that one writes 22 % and not what everyone really does on this pale blue dot, which is 22%. It doesn’t matter what symbols were used back in the horse & buggy days where steam engines were the fastest things around. We don’t try to change the world here as volunteer editors on Wikipedia; we simply reflect the facts. And we also don’t put undo weight on side issues, like writing here that The proper way is to say “I am making a 3 g_n turn.” The real world doesn’t follow this and we won’t be writing that it is the “recommended” or “proper” practice. As you may have noted, this article is not titled g_n-force. We might mention this in a History section (if we manage to get that far). Greg L (talk) 04:43, 15 January 2009 (UTC)[reply]

The cover photo on "Rocket Propulsion Elements" shows NASA's Space Shuttle; I guess Mr. Sutton thinks that the folks at NASA aren't total nitwits. Wolfkeeper, you are right that his book uses g in italics,[1] but this is just one book. You weaken your position by dismissing the agency that built the Saturn moon rocket as inconsequential to the field of rocketry.

The references in this article are weak. The first for "The Canadian Style, Dundham Press" is incomplete. I could not find anything about this book or the publisher. Does it exist? A reliable source must be verifiable. The second has a Google book search to show the "gee" is common for acceleration. Most of the hits are fiction books. I am not sure that a raw Google search is a valid reference.

Wolfkeeper, you will need to find some reliable sources to show that the italic g is more common than the "American-only" practice of the roman g. Remember; most readers of the English Wikipedia are from the evil and ignorant United States. - SWTPC6800 (talk) 06:43, 14 January 2009 (UTC)[reply]

We don't have a policy of tailoring things for most readers; otherwise the entire wikipedia would be written in American english, and would have to be rewritten if our demographic changed. Note that there are far, far more English speakers in the world than are in the UK or North America. What's really happening here is that the sources picked for this discussion gave undue weight to America (perhaps unconsciously), and this has lead to this discussion very much getting off on the wrong foot.- (User) Wolfkeeper (Talk) 14:00, 14 January 2009 (UTC)[reply]

• I'm here from the MOSNUM discussion. It strikes me that even the Canadian manual accepts or strongly implies a non-italicised 'g' is the universal default, only requiring italicisation when there is conflict. That being the case, I have changed the text accordingly. I feel that anyone who strongly feels g (gee in italics) is the default or international norm should validly source it. A reliable source should state specifically that it is used predominantly in its italicised form (and in what context, if nexessary), with a footnote naming the source and including the proper citation - we are obliged to be so specific as there may be others which contradict it. I do not feel mere use of ital-gee in any given textbook, without explaining the scientific notation, is sufficiently NPOV - it is even less justifiable seeing this appears to be strongly contested, and with good reason. Ohconfucius (talk) 07:19, 14 January 2009 (UTC)[reply]

• Wolfkeeper et al.: I believe that Greg is quite right to insist that "g" not be italicised. He has long and broad experience in science writing, and his views transcend any one variety of English. Broader issues that cover such italicisation have been discussed extensively at MOSNUM talk and have been resolved such that "g" is rendered in roman face. Tony (talk) 09:33, 14 January 2009 (UTC)[reply]

The 'valid examples' he has given are universally American-centric or advertising copy and very poor quality. The convention is because of the SI system, but is not part of the SI system. He started off the discussion with threats of applying bots, and has been unreasonably argumentative, and has employed ridiculous arguments such as referencing articles that are specifically about the SI system that have nothing whatsoever to do with the issue in hand. He also started off with accusations of poor faith, that I was 'trying to change the world', when the evidence is actually to the contrary, that he is trying to introduce a non NPOV position, and he has not got any better even when quite reasonable references to its use have been given. It wasn't as if I had to struggle to find these references either, and related constants such as gn are wherever possible specified in italic form, even in the SI documents. In short, I want him to go away now, I don't think I should have to put up with this kind of bad faith garbage in the wikipedia.- (User) Wolfkeeper (Talk) 12:57, 14 January 2009 (UTC)[reply]

This started as a discussion in WP:MOSNUM. The point is that the canadian guideline is probably binding on us in the following way: we cannot predict when the 'g' unit is used whether a gram will later be in use elsewhere in the article. Therefore to keep the units distinct, it might a good idea to indicate that this is the preferred form in the wikipedia, without stating that other forms are actually wrong. I believe that that is the logic that is used by Sutton in using the italic g; no author would want to have to go through and check each page, and I don't think that we should either when authoring the wikipedia. So in my view the house style should be italic because of our common use of SI units, anything else is going to be too confusing and inconsistent. But other uses aren't wrong.- (User) Wolfkeeper (Talk) 13:46, 14 January 2009 (UTC)[reply]

• Wolfkeeper, you are POV-pushing because you want something to be so. Wikipedia always goes with most-reliable sources. I’ve proven above that this planet’s manufacturers of accelerometers, academia publishing medical papers on g-force-induced bodily injury, and the world’s two largest space agencies (NASA and ESA) all use roman g exclusively. I’ve been patient in responding to your objections. You poo-poo’d NASA as for not knowing their butt from a hole in the ground and being “American”, and for being an organization that is only slowly adopting the SI. Then I showed you that the European Space Agency uses roman g. That didn’t seem to impress you either because here you are ranting about how it’s better as italic. Doesn’t matter.

  The problem here is there is a g proponent on Wikipedia who desperately believes g should be used and hopes the world will fall in line. The trouble, is, it is the other way around, Wikipedia follows the way the real world works. Notwithstanding the overwhelming evidence that the world-wide practice is overwhelming to use roman g, you want to state that is ‘most commonly’ or is ‘supposed’ to be g because of one, thoroughly forgettable book and a poorly referenced—and probably misquoted—passage from a Canadian Government manual of style that you’ve obviously never even seen yourself because you can’t cite the page and the entire text on that page. Now…

  This state of affairs is utterly absurd. The world isn’t using g_n or any other suggestions by dueling standards bodies; as you are acutely aware, this article is titled “G-force”, not G_n-force. This article will follow the practices universally observed by all real-world, authoritative sources on this issue. When you can show me that—world-wide—most manufacturers of accelerometers use italic g on their data sheets, and when you can show me that the world’s two space agencies do the same, then this article will go with italic g.

  If you are so concerned about “confusion with g for gram”, you’ve got my blessing to write the whole paragraph about how to avoid that. Note that the manufacturers of accelerometers have chosen to just write on their spec sheets that the weight of their devices are “0.03 kilograms”. I suggest that you follow their lead when writing that section instead of insisting on blazing a new path for the manufacturers and ESA and NASA to follow; they seem to be doing just fine without the help. Greg L (talk) 16:47, 14 January 2009 (UTC)[reply]

I note that you are continually mischaracterising my position to an extreme degree, worse, you also are misquoting wikipedia policy.- (User) Wolfkeeper (Talk) 17:20, 14 January 2009 (UTC)[reply]

You say: Wikipedia always goes with most-reliable sources; but that's simply wrong. The Wikipedia is dominated by WP:NPOV which says that all notable positions are represented. That means you do NOT get to roll out bots and change the entire wikipedia to match your POV of what the majority (sic) real-world sources say when there are notable sources to the contrary.- (User) Wolfkeeper (Talk) 17:20, 14 January 2009 (UTC)[reply]

And I can only request again that you be a lot less tendentious in your discussion style here, it is in no way helpful. Please assume good faith.- (User) Wolfkeeper (Talk) 17:20, 14 January 2009 (UTC)[reply]

I also found it particularly amusing that Greg_L attempted to rewrite the introduction to define g-force incorrectly. It appears he doesn't even know what g-force is, never mind whether it is italic or not! If g-force was a simple measure of acceleration, then I would be sitting in a 0g environment, but in fact my g-force is 1g. It's actually the acceleration relative to the local gravitational field strength measured in multiples of g0, or some such definition.- (User) Wolfkeeper (Talk) 17:53, 14 January 2009 (UTC)[reply]

• Exactly: “or some such definition”. I see why this article is in need of wholesale repair. As noted below in the following section, you haven’t understood all this time that gravity is an acceleration that is absolutely identical to, and indistinguishable from, an inertial acceleration. See General Relativity. Please stop ranting and start listening. Greg L (talk) 20:00, 14 January 2009 (UTC)[reply]

My original comment (see waaay above) was copied over from MOSNUM, so it lacks a bit of context here. I originally came to see what was happening because of a message on MOSNUM. However, what I can say is:

• This article as a whole lacks scientific rigor. A lot of the dispute revolves around the fact that a lot of people are unclear what it is being talked about.
• The name of the article itself is a misnomer. G (or g) is not a force, it is an acceleration due to gravity.
• The symbol g is not a unit, it is a quantity. By itself, g is a variable who's value changes from place to place.
• The symbol g in its non-italicized form conflicts with "g", the SI symbol for gram, so it cannot be used in articles using "g" for gram. Since SI is the global standard system of units, that is a serious issue.
• What is talked about here is not g, but g_n, (which is the official standardized average value of g on Earth) as recognized by the International Bureau of Weights and Measures (BIPM) and the US National Institute of Standards and Technology (NIST).
• The official value of g_n, which everyone uses, was adopted by the Comité International des Poids et Mesures (CGPM) in 1901. For the resolution, see here. Note that it was used in defining the now obsolete unit kilogram force.
• For the NIST version of g_n, see here. Note that it is listed under "Fundamental Physical Constants" and not "Units".
• See also the NIST list of conversion factors see here Note the line "Caution: The units listed in column 1 are in general not to be used in NIST publications", and that the first unit listed is "acceleration of free fall, standard (g_n)"
• NASA is not really a reliable source of ways to handle units. In 1999 they actually had a satellite burn up in the atmosphere of Mars because their satellite was designed in metric units, and their sub-contractor transmitted the course corrections in imperial units.
• I quoted the Canadian Style manual because Canada is something of a microcosm of the world as a whole. It has two official languages and officially uses the SI system, plus unofficially both the American and British imperial systems.
• The Canadian Style manual reference is: Public Works and Goverment Services Canada (1997). The Canadian Style - A Guide to Writing and Editing. Dundum Press Limited. ISBN 1-55002-726-8. {{cite book}}: Check |isbn= value: checksum (help).
• The Canadian Style manual follows the SI Standards set by the BIPM. The BIPM sets the global standards for the SI system.
• The US NIST follows the BIPM standard as well, with minor variations.
• For the NIST guide to using the SI system from the American perspective, see here.
• In the NIST Guide to Using the SI System, be sure to read pages 39-44 on "Writing unit symbols and names, and expressing the values of quantities", because it is the official American standard for writing scientific papers.

Cheers.RockyMtnGuy (talk)

• You clearly haven’t read all the threads here. Every one of your points has been addressed and refuted. As was amply demonstrated with our three-year experiment to follow the IEC’s proposal on binary prefixes, where we wrote “kibibyte” (KiB) instead of what the world really uses: “kilobyte” (KB), it is wrong for Wikipedia to embrace standards that the world ignores. You know that. NASA and the European Space Agency and the manufacturers of accelerometers and the distributors of accelerometers and anyone who does scientific or medical work uses “g”. We follow the way the world works. Greg L (talk) 18:22, 15 January 2009 (UTC)[reply]

I'm not convinced by your argument here Greg_L. The very first book I grabbed (Sutton) did follow this italic convention, and this has been verified by others here. Is that pure coincidence? I don't know without further research; but it's a bit strange, I would not have expected Sutton and the other authors to make up the convention. I checked the ESA page you indicated, and it did not support your claims either, it didn't appear to be talking about g-force, it appeared to be talking about standard gravity and (eroneously) calling it 'g' force.ESA’s GOCE However RockyMtnGuy claims that the Canadian Style guide supports this usage, but this has not been verified by others here. Can he quote the exact passage that supports this?- (User) Wolfkeeper (Talk) 19:11, 15 January 2009 (UTC)[reply]

• It doesn’t matter what the BIPM or the Canadian government says, nor the Liberian government says, nor what the IEC says (the people who proposed “kibibytes”). We do not follow what the IEC says about the binary prefixes (MiB v.s. MB) in our computer articles because the real world does not use them. We tried that for three years before realizing it was a collosal mistake to have done so when no computer manufacturer and no computer magazine used them. Nor do we follow (*even*) the BIPM if their recommendations aren’t observed in the real world. We completely flout the BIPM when they say it is cm³ or ml when we write the Kawasaki 750 cc motorcycle engine. Why? Because the real world doesn’t work that way. Want another example? According to the BIPM’s SI manual of style, 5.3.7 Stating values of dimensionless quantities, or quantities of dimension one, When it [the percent symbol] is used, a space separates the number and the symbol %. This practice has not been well adopted with regard to the % symbol, is contrary to Wikipedia’s Manual of Style, and is not observed here. Wikipedia does not require us to write we had 22 % observance of common-sense rules by editors on Wikipedia just because some standards body says we should. Don’t start poo-pooing the European Space Agency now. They write on their Web site on the gravity experiment probe as follows: At school we generally learn that g = 9.8 ms–2. We all know what they mean. And these guys are as SI compliant as anyone else you can point to.

  Now give it up. I’ve shown that the world’s space agencies use roman g (not g_n) and so too do the world’s manufacturers of accelerometers, as well as any real-world scientific uses of accelerometers. You don’t have to like the fact that the symbols for gee and gram are the same; just realize that this is the way the real world works. And to also accept that goal for any encyclopedia is to communicate with minimal confusion so that readers can learn about a subject and are primed as well as possible to learn even more in their studies elsewhere. We don’t accomplish that end by using symbols or units of measure that aren’t used in the real world. Greg L (talk) 20:42, 15 January 2009 (UTC)[reply]

It does matter what the BIPM says, because they set the international standard for metric units. Since "cc" is an obsolete symbol for "cm³, we should convert all instances of the former to the latter. However, nobody I know uses "kibibytes", so I think we can ignore it, and the Canadian Style manual specifies that there should be no space space between a number and the % symbol, so the Canadian government disagrees with the BIPM on that point. In addition (this is probably too radical an idea for Wikipedia), the Canadian Style manual says that, while SI unit abbreviations should never be followed by a period, imperial unit abbreviations should always be followed by a period (e.g. "cm³" versus "cu. in."). However, the whole point is to avoid ambiguity in articles. Since the SI system uses most of the Roman alphabet and some of the Greek alphabet, the normal solution in scientific papers is to use italics to distinguish letters used for quantities from letters used for SI units. Writing for school children is a different issue.RockyMtnGuy (talk) 04:22, 16 January 2009 (UTC)[reply]

• I agree that we're not formally bound by any standard, but we should at least evaluate existing standards before picking one for ourselves. Your idea Greg_L basically seems to be that you tell us what we are going to do, and that you ignore any existing conventions that are contrary to that? Who died and made you God? Nobody. If RockyMtnGuy can quote worldwide standards, then we can at least evaluate them. We may or may not decide to follow them (at the moment I'm leaning away from italic form somewhat), but Just Do It Greg_L's Way Because He Says So(tm) is a heap of garbage that I cannot ever agree to. FWIW you don't even follow the editing standards of the wikipedia's talk page; exactly who says you get to stick a * in front of every comment you make???? Why should we trust you to help set the wikipedias guidelines when you make up your own?- (User) Wolfkeeper (Talk) 05:09, 16 January 2009 (UTC)[reply]

• P.S. I’ll take something back, RockyMtnGuy, when I responded to your last post. When you wrote This article as a whole lacks scientific rigor, I couldn’t agree more. In fact, it is an understatement. Greg L (talk) 23:21, 15 January 2009 (UTC)[reply]

True, the problem is lack of rigor and clarity in the article. It is very foggy on the concepts it is talking about. You need to use a style guide which allows rigor and clarity to be achieved, keeping in mind that this is a globally readable medium.RockyMtnGuy (talk) 04:22, 16 January 2009 (UTC)[reply]

Just my two cents. A physical quantity and a unit can be equal by definition and still stay a physical quantity and a unit. For example, the NIST list of CODATA recommended values for physical constants defines one of them as . I guess the same applies here: g_n = 1 g. I'm not going to insist more on this because 1) I'm already busy enough, and 2) I barely know that this unit of measurement exist. But, given that I often read things I could be expected to be very marginally interested in, just because of boredom (that's more-or-less what my Sewer Cover Barnstar says), if there was an exception to the rule of upright symbols for units I would likely (i.e. about 25% chance) have sometime encountered it, and given that I'm a markup fanatic (i.e. ones who uses boldface for vectors even in handwriting), if I had ever encountered it I would very likely (i.e. about 90% chance) remember about it. (This doesn't prove that no such exception exists, of course.) -- Army1987 – Deeds, not words. 11:03, 16 January 2009 (UTC)[reply]

When I read great G or non italic g for g-force then know I that the writer have no glue about physics or works sloppy or have problem with the code page (contain no italic). First G stand for the gravitational constant or weight, but not for g-force! 2.2 SI derived units What mean [2] ? Right gn and CODATA the same. NASA (who mixed gravitional constant and g for g-force) and Honeywell are not an Institute for Standardization! The Internet is the wrong place for this recherche, through lack of the right codepage! We should take a look in physic books and technical formula libraries (Gieck and Bosch etc.) all wrote g small and italic. Kinematik Kinematik [3]or Gerthsen Physik ISBN 978-3-540-25421-8 or Dr. Ernst J. Feicht * Dr.Ulrich Graf ISBN 3-7632-1617-0 Page 58 etc. --HDP (talk) 18:04, 16 January 2009 (UTC)[reply]

An editor added a fact tag with the comment "g-force isn't actually a measure of acceleration, it's acceleration relative to gravitation field." This is not true. F=ma (newtons 2nd law). gforce & mass = force. Thus, by definition, gforce = acceleration. It is expressed in units (gs) that are equal to 9.8 m/s2 per g. Hipocrite (talk) 17:53, 14 January 2009 (UTC)[reply]

Sorry, that's wrong. I'm sitting at 1g but my acceleration is zero. Acceleration is m/s^2; m/s = zero.- (User) Wolfkeeper (Talk) 17:57, 14 January 2009 (UTC)[reply]

You raise a good point that gforce has a "base" unit of -1. I've made that clear in the intro. Hipocrite (talk) 18:01, 14 January 2009 (UTC)[reply]

Do you have a reference for that either????? In my opinion it's also clearly wrong and still uncited to boot.- (User) Wolfkeeper (Talk) 18:14, 14 January 2009 (UTC)[reply]

I don't see how it dosen't follow from everything else written. Perhaps you could define what you believe the g-force to be, simply worded. Hipocrite (talk) 18:15, 14 January 2009 (UTC)[reply]

I'd like it to be defined the same way as a reliable source, hence the citation request.- (User) Wolfkeeper (Talk) 18:23, 14 January 2009 (UTC)[reply]

Good to go - "Although the term "g force" is often used, the g is a measure of acceleration, not force." [4] Hipocrite (talk) 18:29, 14 January 2009 (UTC)[reply]

I don't find that that is a definition, more of a comment. And a lot of the article seems to be talking about acceleration due to gravity which is a distinct concept to g-force as discussed here.- (User) Wolfkeeper (Talk) 05:01, 16 January 2009 (UTC)[reply]

• Hipocrite, is entirely correct. The g is a unit of acceleration. It is 9.80665 m/s². Period. Period. Regardless of axis. The baseline you want to measure it against depends on the need, just like pressure may be gage pressure (psi-g) or absolute pressure (psi-a). In the case of the former, the pressure is measured with respect to background atmospheric. You might measure 30 psi-g in a tire but there is 44.7 psi-a (at nominal sea level) in absolute terms. The same applies for accelerations.

  Usually, vertical accelerations for dynamic situations are measured with respect to barycenter of the Earth. Thus, at sea level at around 53° latitude on the geoid, one will be experiencing an acceleration of 1 g when one has no further vertical acceleration with respect to the ground. If one accelerates at 9.80665 m/s² in a plane with respect to the ground, the total acceleration is 2 g. However, if one has an inertial navigation instrument, its three-axis accelerometers are zero’d when it is stationary with respect to the surface of the Earth.

  Wolfkeeper, you are displaying WP:OWN issues here and are also exhibiting a breathtaking lack of understanding of basic physics when you wrote Sorry, that's wrong. I'm sitting at 1g but my acceleration is zero. Acceleration is m/s^2; m/s = zero. Einstein showed that with his “light beam across an elevator” thought experiment that an inertial acceleration relative to the Earth’s surface is identical to and indistinguishable from gravity; they are one in the same. F = ma does not go out the window, Wolfkeeper, depending upon the axis one measures. A 1-kilogram object sitting stationary on the floor, per F = ma, is being accelerated at 9.80665 m/s² due to gravity and that is why it generates a gravitational force of 9.80665 newtons downwards.

  I’ve got a lot more work ahead of me to fix this article. If your writings here on this page, Wolfkeeper, are an accurate representation of your knowledge on basic physcis, then you obviously don’t yet understand enough to be doing any good here right now. I suggest you start with General relativity to understand something elementary like how gravity is an acceleration—like any other—and that Hipocrite is entirely correct. I’ve reverted your edits since they are entirely incorrect and are POV-pushing. This article is sorely lacking and needs to be consistent with MOSNUM, basic scientific principles, and the way the rest of the world obviously and clearly works. Greg L (talk) 19:14, 14 January 2009 (UTC)[reply]

Feel free to remove citation requests and not cite anything, go right ahead. Is there a single wiki policy you haven't broken multiple times today????- (User) Wolfkeeper (Talk) 19:30, 14 January 2009 (UTC)[reply]

• Wikipedia is a collaborative writing environment. Friction between editors goes way up quickly when an editor isn’t listening to what others are saying. Sit back and be patient. The real world calls and I have stuff to do. Fixing articles takes time. I do my homework and when all is said and done, this article is going to be correct; factual; balanced with respect to reflecting the most common, real-world practices; and will be well-cited. In the mean time, I suggest you afford Hipocrite much more latitude than you have so far; he, at least, has the basics of F = ma down pat and that will be a damn good start here. Greg L (talk) 19:37, 14 January 2009 (UTC)[reply]

You're the biggest hypocrite I have ever met on the wikipedia, and I have been here a long time, by a very long way indeed.- (User) Wolfkeeper (Talk) 19:40, 14 January 2009 (UTC)[reply]

Remain civil, you two. This is way overboard. Can you each explain what the problem here is, clearly and succinctly? Hipocrite (talk) 19:45, 14 January 2009 (UTC)[reply]

• Wolfkeeper, I’m leaving your “citation” about the Canadian government’s manual of style in place at the moment in order to give you sufficient time to gain access to it. Based on your continued silence in the face of my repeated requests to cite the page number and quote all relevant text pertaining to italicizing, it appears you are currently only assuming what it says on the subject. When I cite Web pages, I provide a link so readers can see it themselves. If I cite books, and if it is practical to do so (one or two succinct points of fact), I quote the passage. Given that all the world’s authorities on acceleration (manufacturers of accelerometers and the space agencies) use a roman g, we need to make sure what the Canadian government manual of style really and fully says on the subject. That should give you something to focus on instead of uncivil name-calling. Greg L (talk) 19:52, 14 January 2009 (UTC)[reply]

• The manual of style is avaliable on books.google.com at [5]. I reviewed the text, searching for "gforce" "g force" "g-force" "force" "SI units" and "italic." The only relevent text I found was in the italics section, 6.11 - which does not appear to substantiate italicizing "g" the unit. Hipocrite (talk) 20:34, 14 January 2009 (UTC)[reply]

• Thank you very much, Hipocrite. There is indeed the potential for confusing g with gram, but the issue seems more imaginary than real based on real-life experiences with the space agencies and anyone else who deals with acceleration. Examine this hypothetical: The lake in 1999 measured only 2.6×10¹³ litres but we measured 2 gal notwithstanding its lack of volume. What do you expect when you click the links? Did I mean …but we measured 2 gal or …but we measured 2 gal? Clearly, the scientific world marches on notwithstanding the potential for confusion.

  The simple solution in those relatively rare instances where small amounts of mass needs to be discussed within a document that is focused primarily about accelerations is to use the SI base unit kilogram (or the gram) and to write out the unit of measure. This is in keeping with the actual, real-world practices of the manufacturers of accelerometers. That should be enough to ensure midwives don’t weep, boils don’t appear on our faces, our goats don’t lie down in the fields, and our crops don’t wither. For now, I am removing the citation as it appears to be false. So far, I am still on the first paragraph of the article. A huge amount of work remains. Greg L (talk) 20:50, 14 January 2009 (UTC)[reply]

• What do you think of that lead paragraph, Hipocrite? I have endeavored to get a lead that is absolutely factual and succinct. Have I succeeded? If so, we can build from there. I’ve gotta go right now. Thanks again. Greg L (talk) 20:54, 14 January 2009 (UTC)[reply]

Please don’t disrupt Wikipedia to make a point. Basic physics should not have to be explained. Your above writings demonstrate that you not only have insufficient understanding of physics, you have an incorrect understanding of physics. Notwithstanding that I shouldn’t have to educate you here (simply getting out of the way and letting me correct this article should suffice), I will nevertheless provide a short tutorial here. Sit back and learn. The measure of g-force is the measure of accelerations. Period. Inertial acceleration is precisely the same as gravitational acceleration. Even for a light beam, gravity and inertial acceleration are the same (see General relativity). If you can’t wrap your mind across that concept, go get yourself a three-axis accelerometer—even an iPhone will do—and tilt it around and see what happens. Then go jump off a roof (please do so safely) and see what happens. You will see that you can make any axis on the accelerometer respond to one g of Earth gravity just as you can by getting into an automobile and hitting the brakes. There will always be this pesky “Earth gravity” signal that you can make leak into any of the axis depending on how you hold it.

I’ll be doing most of my repair on this article starting over the weekend. Greg L (talk) 19:11, 16 January 2009 (UTC)[reply]

P.S. I fully intend to (slowly) get this article good enough for Good Article (GA) status. I’d tell you about the last article I worked on, which recently earned GA status, but I’m afraid you’d try to go teach the world about how it’s all screwed up over there too. Getting this to GA will take a lot of time since this article has parts that are fouled up beyond all recognition, and has other parts that make a point in a very, very poor way. This article clearly has been the product of too many drive-by shootings over the years by too many amateur I.P. editors, as well as by a certain registered editor who hasn’t understood all this time that gravity is an acceleration that affects accelerometers. This article is in need of serious repair and revision. That means I’ll try to add content where possible. But some parts will be deleted as new passages slowly expand and later replace them. Don’t panic and leave your propensity for WP:OWN behind. Further, part of getting an article to GA status is to have an attractive, nearly decorative, photo with an illuminating caption. I would greatly appreciate it if you would stop snipping away at my heels as I do this. Greg L (talk) 19:37, 16 January 2009 (UTC)[reply]

I simply asked you to cite what you wrote. Apparently you can't do that or you wouldn't be trying to condescend to me. I find this... regrettable.- (User) Wolfkeeper (Talk) 19:40, 16 January 2009 (UTC)[reply]

And ummmm, no what you wrote is not quite right. When you jump off there's no signal, nothing leaks in, because you're following the geodesic (ignoring slight wind resistance). And that's one of the problems, gravity isn't an acceleration as far as g-force is concerned, but the reaction to it is if you stand on the ground or whatever. But you don't even need GR theory for this article, and I'm not convinced it's helpful to a lot of people, but mentioning it somewhere might be a good idea.- (User) Wolfkeeper (Talk) 19:40, 16 January 2009 (UTC)[reply]

• No you are entirely wrong when you write “gravity isn't an acceleration as far as g-force”. Why do you think accelerometers indicate 1 g when they are sitting on a desk? Greg L (talk) 20:08, 16 January 2009 (UTC)[reply]

Yeah, 1g upwards, because the desk is giving a positive g relative to the geodesic. The gravity acceleration is downwards. You're scaring me here Greg_L; this is really basic stuff.- (User) Wolfkeeper (Talk) 20:15, 16 January 2009 (UTC)[reply]

The g-meter would usually invert it for display purposes though to give an effective gravity direction. But the acceleration is actually upwards. You could mount the accelerometer on a rocket and adjust it to stay at the same altitude and it would give the same reading.- (User) Wolfkeeper (Talk) 20:19, 16 January 2009 (UTC)[reply]

Unfortunately for you I have actually studied advanced physics including quantum electrodynamics and I believe I actually have an entirely adequate understanding of relativity, curved space, geodesics, simultaneity for the purposes of this article etc. etc. My favourite paradigm of quantum theory is the many worlds theory, as supported by Feynman, and no, I don't understand it any more than he does (OK, less.) Any questions? Oh, and you might like to mention that you are assuming GR theory in the introduction since otherwise it makes absolutely no sense, most readers will probably assume you are talking about Newtonian mechanics since you aren't mentioning curved space-time, and there is also the sticky question of the likely readers not actually being up on GR, and the introduction actually deceptively implying things that aren't true if they don't realise that.- (User) Wolfkeeper (Talk) 19:40, 16 January 2009 (UTC)[reply]

FWIW give me any more of this shit and I will simply revert the article. Unverifiable content can be removed at *any* time, and you've just added a whole bunch, and no references. Have a nice day.- (User) Wolfkeeper (Talk) 19:40, 16 January 2009 (UTC)[reply]

I just got a message on my talk from some guys working on WP:DICK apparently they want to do a feature article on you Greg_L; are you interested? They seem really, really keen.- (User) Wolfkeeper (Talk) 20:02, 16 January 2009 (UTC)[reply]

• I have amply demonstrated above that the standard, world-wide practice amongst all manufacturers and distributors of accelerometers and as universally observed by scientific and medical researchers, and by NASA (which you poo-pooed as being “American”) and by the Europan Space Agency (all of these have been cited above), you roman lowercase g for the unit symbol g. You may not simply choose to ignore this when the article states as follows: “The gee is precisely equal to 980.665 gal. The world-wide standard practice has the unit symbol g as lowercase and roman (upright).” This is indisputably true. Stop editwarring. If you want to prove that the world-wide, standard practice is to use italic g, prove it. There also seems to be a chronic problem with your propensity to nebulously cite sources (such as the Canadian government manual of style) only to have other editors find it on Google Book and prove that it says no such thing. Wikipedia can’t work when editors operate this way. Greg L (talk) 20:18, 16 January 2009 (UTC)[reply]

• As for your above allegation that I just got a message on my talk from some guys working on WP:DICK apparently they want to do a feature article on you Greg_L; are you interested? They seem really, really keen., that appears to be a lie. I just checked the history of your talk page. There is no record I can find of someone who is working on WP:DICK complaining about my behavior. All I could find on your talk is this recent complaint about your editwarring here. And I also see there is this recent complaint about your editing against consensus. Note also our proving that your supposed “citation” to the Canadian government manual of style was either a purposeful fabrication or an error. All in all, I’m seeing an extremely troubling pattern here with you. Greg L (talk) 20:33, 16 January 2009 (UTC)[reply]

Really? It's not there? I guess the admins must have deleted it or something; they can do so. Oh well. On the Canadian manual of style I was lead to believe that it stated that, but I did not have it to hand to verify. The Sutton book I did have, and I was able to show that it did indeed support the usage. Your comments which suggest a shaky understanding of the physics of accelerometers and g-force and your idea that you don't need to cite are still giving me some cause for concern though, but would not necessarily indicate a poor outcome. To be honest I'm glad to see someone enthusiastic about this article, although your attitude to your fellow editors could do with some... adjustment I feel.- (User) Wolfkeeper (Talk) 20:57, 16 January 2009 (UTC)[reply]

Wrong with the ESA you should look at the hires picture left side, g italic so what? This lemma is shure not GA. Internet and Google is the wrong place for the recherche for the Italic question. Better sources a physics books for university, only this is the standard. Fact is g can confused with g. Then for mathematical loosers, between digit and g is no space or you need a multiplication sign! --HDP (talk) 20:42, 16 January 2009 (UTC)[reply]

Then is gal obsolete and should not used! Gal is as unit outdated! Only earth sciences use gal.--HDP (talk) 20:49, 16 January 2009 (UTC)[reply]

• “Obsolete”? Wrong again. Since 1978, the BIPM has approved the gal for use with the SI. Please note that the BIPM has also done this with other non-SI units such as gauss, tonne, liter, hour, and minute. (BIPM, Table 6 and BIPM, Table 9). Odd—that apparently “obsolete” unit, gauss; my company just bought a magnetometer a few months ago. It is calibrated in gauss. Note too my autosignature at the end of this post, which contains hours and minutes; units that are also not officially part of the SI but are recognized as acceptable for use with the SI. The gal certainly has good company. Greg L (talk) 00:08, 17 January 2009 (UTC)[reply]

The gal is not part of the International System of Units! [6]

• • I made some edits to the article before reading this. It's clear you are having a disagreement; are you able to state concisely what the exact nature of the disagreement is? I may be able to help as I'm also science-trained and have an interest in aviation, which often uses the unit. --John (talk) 06:26, 17 January 2009 (UTC)[reply]

• Hallelujah. Semper Fi. Welcome. And an admin too!

  Per a recent post on my talk page (∆ here), Wolfkeeper might no longer respond here. But, in a nutshell, he has been arguing that g-force is not a measure of acceleration per se, it is the measure of inertial accelerations and ignores the effect of gravity. Specifically, he wrote in an edit comment while adding a {fact} tag as follows: g-force isn't actually a measure of acceleration, it's acceleration relative to gravitation field and then expanded upon it here on this talk page by writing I'm sitting at 1g but my acceleration is zero. Acceleration is m/s^2; m/s = zero. I know. But he wrote above that I have actually studied advanced physics including quantum electrodynamics.

  He has also been arguing that g is supposed to be italicized in order to avoid confusion with the symbol for gram. Perhaps that ought to be the case. But it isn’t. Further, the basis for making this claim hadn’t been cited since this article first began—for years; the “citation” was only alluded to here on the talk pages as being advise from a Canadian government manual of style. When challenged recently, he cited the manual of style (here) and the publishing house, but couldn’t quote the text or page when repeatedly asked. It was finally shown via Google Book search (Hipocrite (talk) 20:34, 14 January 2009 post) that the manual says no such thing. I think my litany of citations are sufficiently authoritative to buttress the obvious.

  I’ll be wading into this article over the weekend; it needs work. Your assistance here will be quite welcome. Thanks for the “trim”. Greg L (talk) 07:29, 17 January 2009 (UTC)[reply]

I'am a Dipl.Ing and not nowdays common lowcost master ing. --HDP (talk) 07:28, 17 January 2009 (UTC)[reply]

• Say what?!? Greg L (talk) 04:18, 18 January 2009 (UTC)[reply]

They are two different things. The symbol for standard gravity is g_n. One g, as it applies to g-forces, is equal to g_n. This is all cited in the article. Greg L (talk) 23:19, 16 January 2009 (UTC)[reply]

Notation: variablen and constants writen always kursiv = italic point 2 [7]Maybe a little bit to high for some here, from an Experimental Physics book. g = g^E-Ω²*R that is the effective gravity Experimental Physik 3.194, 3.197, 3.199. That shown g^E and g must writen italic in context! That indicate that NASA and ESA use a non standard notation! --HDP (talk) 11:25, 17 January 2009 (UTC)[reply]

No, one is a quantity and one is an unit. You can write m_u = m(¹²C)/12 and that would be an equation about quantities, but this doesn't mean that the unit isn't 1 u (see atomic mass unit). I don't know about this particolar unit, the gee, but "That shown" and "That indicate" are non sequiturs. -- Army1987 – Deeds, not words. 16:59, 17 January 2009 (UTC)[reply]

• Precisely. Let’s take it as an article of faith that NASA, ESA, and JPL, which are all heavily populated by scientists with advanced degrees and Ph.D.s, actually know what they are talking about. Let’s also acknowledge that Honeywell [8], a world-wide, leading manufacturer of industrial and military-grade accelerometers, knows what they are doing.

  This is not complex. My younger brother is a pilot and I subscribe to Aviation Week & Space Technology, which is the preeminent periodical for the industry. It contains advertisements for missile defense systems, commercial launch services, and fighter planes. It is subscribed to by industry and government leaders throughout the world. They write “a 9 g turn”.

  There will never be a way for me to prove it—and I certainly might be wrong about this—but I will forever suspect that at least some of the editors responsible for this knew full well that the standard practice observed throughout the world is roman g, but they simply believed the practice unwise and hoped to promote change in the way the world works by stating a falsehood as a fact.

  The only people who were writing “a 3 g roller coaster” were school children who had the misfortune of landing here and being exposed to misinformation. Now fixed. Greg L (talk) 21:18, 17 January 2009 (UTC)[reply]

• I certainly confirm that all the aviation magazines I read and all the books, as far as I can recall, use regular upright g to show g-forces. I can see the argument for using g to avoid confusion, and it may well be done that way in some physics books, but I think we should always follow the sources. On a completely other note, I know the RAF call their anti-g garment their "turning trousers"; if I can reference that I may try to add it to the article. --John (talk) 04:21, 18 January 2009 (UTC)[reply]

The chatty style of the first two sections -- "Understanding the nature of the measure" and "Gravitational and inertial acceleration" -- is inappropriate for an encyclopedia article. —Preceding unsigned comment added by 86.134.30.255 (talk) 04:54, 18 January 2009 (UTC)[reply]

• Agreed. I questioned whether the “Why?” was encyclopedic when I wrote it. Now fixed. I’m not really seeing anything else. So, I.P. editor from London, please be specific about any remaining un-encyclopedic passages you feel still need to be addressed. Greg L (talk) 04:58, 18 January 2009 (UTC)[reply]

• Yeah, agreed doubly. I made the edits (again!) before reading this, but I hope they go some way to alleviating your concerns. Specific suggestions are always especially welcome here, as Greg says. --John (talk) 05:22, 18 January 2009 (UTC)[reply]

What are we to do with G-force#Human_g-force_experience. It reads like a trivia section and is a citation nightmare. An editor today put a {fact} tag on an assertion that a wristwatch is rated for shock of up to 7 g. So I checked into it and found that watches are rated for shocks of 5000–7500 g. What a colossal goof. That was just one item and it took a fair amount of time to dig up the facts. I could abandon the article now, but my style is to stick with these things to the end. I think much of the stuff—and there is a lot of it—in this lower half of the article could be made much more succinct and tied together better. Who here is married to all those bullet points? Greg L (talk) 04:57, 18 January 2009 (UTC)[reply]

• Agreed. Bullet points are fine for multiple comments in talk (as here), but they make the article look bad. Put it into prose, keep that which can be verified (I'm not against having a few interesting g-based data points on an article about g-force), and lose the rest. Onwards and upwards. It's already looking better, I think. --John (talk) 05:28, 18 January 2009 (UTC)[reply]

• • However, on reflection, the whole latter part of the article is avoidably scrappy. As the article makes clear, transient g-forces (a slap or a sneeze) are inherently more survivable than sustained forces. We need to rewrite the entire thing in a more coherent way, and we need to make any claims of "records" especially well referenced, or we shouldn't be making them. Just my opinion of course. --John (talk) 06:00, 18 January 2009 (UTC)[reply]

• I’m not sure what to do. Excising material is bound to be particularly painful to whoever put it there. However, the majority of the “records” and “greatest ever”s are un-cited. Nor are most of them really needed. Furthermore, this article looks a lot like the Guiness Book of World Records and it’s not supposed to. An encyclopedic treatment of g-force can be thoroughly covered here by touching briefly on a handful of particularly notable special conditions. We could, for instance, do a better job here by touching upon the rate of change of acceleration, which elevator engineers call “jerk”, instead of messing around with what looks like a list of every roller coaster on the planet. As you pointed out, we can continue on with a brief discussion of transient effects. Note too, that this article has a table of NASA g tolerance data, but it would be better if this data was simply an external link in a Further reading section.

  As is typical when I’m in this situation, I’ll probably just add another section, copying from what’s here at times, and afterwards, simply delete redundant and unnecessary sections. That whole Human g-force experience is completely out of hand. Besides, a big list of roller coaster peak g-forces begs to be its own article; it may well be a separate article already. Greg L (talk) 09:04, 18 January 2009 (UTC)[reply]

Yes, the bragging list of roller coaster rides belongs in Roller coaster. This article does need a good thorough review and clean up. Rlsheehan (talk) 16:42, 18 January 2009 (UTC)[reply]

Yes, I agree and have tagged some with a view to removing them if they can't be reliably sourced. See also the new section below. --John (talk) 18:08, 18 January 2009 (UTC)[reply]

I only linked it as it's not that common a word and many people wouldn't know it. How about changing it to "control column" or "joystick"? Probably the latter. I do agree with the sentiment of not having loads of distracting links. --John (talk) 05:30, 18 January 2009 (UTC)[reply]

• Or just “stick”. Any of the three. Your choice based on what you think will be most universally understood without linking. I’ll go ahead and try stick. Change to something better if you like. Thanks for my second “trim.” Greg L (talk) 05:37, 18 January 2009 (UTC)[reply]

• P.S. I ended up with “control wheel”. More formal than “stick”. Greg L (talk) 05:41, 18 January 2009 (UTC)[reply]
  • Nah, I reckon stick was the mot juste there, WP:COMMONNAMES in mind, that's what pilots call it. Great work, keep it up. --John (talk) 05:50, 18 January 2009 (UTC)[reply]

• Thanks again for the second “trim” and tone change. I could see the conversational tone, but couldn’t for the life of me figure out a way to purge it. Greg L (talk) 06:02, 18 January 2009 (UTC)[reply]

• You're very welcome; it's a strength of this medium when we can work together to make this article better. --John (talk) 08:12, 18 January 2009 (UTC)[reply]

This entire section has a fundamental problem. Transient g-forces are much more survivable than prolonged ones. Is there a standard for defining "transient" vs "prolonged"? The airline industry uses dummies to test new designs of seats. Perhaps some of this section belongs in a different article; as it stands it contradicts correct information above it in the article. --John (talk) 18:11, 18 January 2009 (UTC)[reply]

• Beyond the Black Box: the Forensics of Airplane Crashes by George Bibel, John Hopkins University Press, 2008 (ISBN 0-8018-8631-7) has a whole chapter on "Human Tolerance to G Loads and Crash Forces". I'll try to add some stuff from it later today. --John (talk) 19:09, 18 January 2009 (UTC)[reply]

• • I made some major trims, and changed a couple of things around. We don't need a bragging list, as someone said above. The source I quote was based on a survey of over 100 rollercoasters and seems reliable. Please see what you think. --John (talk) 03:19, 19 January 2009 (UTC)[reply]

Transient short-term "g-forces" are better described in the article on Shock (mechanics). Rlsheehan (talk) 03:34, 19 January 2009 (UTC)[reply]

Nice trims, Greg. I restored my reference with the figure 3.5 to 5 g, based on an extensive survey of rollercoasters and in a serious book about aviation safety. It looks so much better with that one sober reference than with all these supposed bests. --John (talk) 04:19, 19 January 2009 (UTC)[reply]

• Thanks. No doubt WP:BOLD, but I agree: nice. Nice enough to actually want to read it now. Greg L (talk) 04:34, 19 January 2009 (UTC)[reply]

• Really good work, Greg. And good suggestion, Rlsheehan, I've posted at Talk:Shock (mechanics) as that text was referenced and it may go quite well there. --John (talk) 05:01, 19 January 2009 (UTC)[reply]

Should we have a "Not to be confused with Big G" or something early on? Or should that be a matter for G-force (disambiguation)?

• Sounds prudent. Will address now unless you beat me to it. Greg L (talk) 04:35, 19 January 2009 (UTC)[reply]

This was added here on January 14 and I think the article has moved on. Any objections if we take the tag down? --John (talk) 05:12, 19 January 2009 (UTC)[reply]

• No objection here. The editor who placed it there has not responded to your request that he state concisely what the exact nature of the disagreement is. He seems to have lost interest and moved on. More importantly, in my view, is the world-wide practices observed by most–WP:Reliable sources are clear as regards terminology and unit symbols. Greg L (talk) 05:29, 19 January 2009 (UTC)[reply]

I must admit the article is now rather pretty but just not correct.

I think to start with that we all agree that accelerometers measure g-force.

Where we seem to differ is that the article claims that an accelerometer/g-force measures acceleration due to gravity. But you can't actually measure an absolute acceleration due to gravity. It's physically impossible.

If they did measure that, then I would welcome an attempted explanation, which would explain why an accelerometer resting on the ground gives a positive-g reading away from the center of the Earth, and why an accelerometer that is falling downwards with gravity gives a zero reading. It's almost as if an accelerometer can't measure gravitational acceleration... "An accelerometer never senses gravitational acceleration." isn't it?

I mean if I have something resting on the surface of the Earth, it's not accelerating. No way, no how. There's an acceleration due to gravity pulling it down, and a force due to the surface of the Earth that is pushing it up, that would give an acceleration (from f=ma) that would cancel the gravitational one, causing it not to move/accelerate.

However, if the accelerometer can't read the gravitational acceleration (because all parts of it are subject to precisely the same acceleration due to gravity, giving no strains on the spring), then perhaps you might consider that that might explain things, since you would just be measuring the upward acceleration due to the upward force of the Earth, the downward one being invisible to the accelerometer.

You just can't get an absolute reading of gravity from an accelerometer. You can get a differential reading though, and that's done routinely in spacecraft; but the most correct and most general explanation is that accelerometers measure, not an absolute acceleration (which is impossible), but proper acceleration.- (User) Wolfkeeper (Talk) 12:08, 19 January 2009 (UTC)[reply]

Why is this such an important distinction to make? Do we have reliable sources for this? --John (talk) 18:40, 19 January 2009 (UTC)[reply]

Because I don't like the idea that we write something that's wrong. I'm sure we could find a really good reference that clears this up (maybe Wheeler's Gravitation covers it). I added a ref to the proper acceleration article that talked about rockets specifically that I found in google books.- (User) Wolfkeeper (Talk) 20:42, 19 January 2009 (UTC)[reply]

• Wolfkeeper, let’s focus on the locus of where we differ. You wrote, above, as follows:

1. Where we seem to differ is that the article claims that an accelerometer/g-force measures acceleration due to gravity. But you can't actually measure an absolute acceleration due to gravity. It's physically impossible.
2. I mean if I have something resting on the surface of the Earth, it's not accelerating. No way, no how.
3. However, if the accelerometer can't read the gravitational acceleration (because all parts of it are subject to precisely the same acceleration due to gravity, giving no strains on the spring)

You cited a post by a member of a model rocketry club, Dave Redell. In attempting to explain how accelerometers work, Dave used some unfortunate wording in describing how one would look at gravity, but he has correct observations of how accelerometers respond to being handled. Further, a fuller quotation than what you provided above is more illuminating. Dave wrote as follows:

        An accelerometer never senses gravitational acceleration.

or more specifically:

        An accelerometer is a device that senses deviation from freefall.

The last sentence of his explanation paints the complete picture of his message point in that model rocketry article. What Dave (“Lunar” member #332) went on to explain is the same thing this article now explains: when an accelerometer is resting on a desk, it is responding to the earth accelerating the device upwards through spacetime and will read 0 g only when dropped and is in freefall. That is why a “stationary”, single-axis accelerometer reads 1 g on earth and the signal goes to 0 g when you rotate it 90°.

If you don’t believe me, John, Rlsheehan, and Army1987, then please go get yourself a 3-axis accelerometer—even a single-axis accelerometer will do. For that matter, a digital kitchen (diet) scale with a stick of butter taped to its platen will do just fine. You will see for yourself that they behave precisely as described here in the first pargraph of Gravitational and inertial acceleration (as well as with the article you cited). You will be able to see for yourself that the only time there are no strains on the spring of a 3-axis accelerometer is when it is in freefall.

When you see this for yourself, then you will abandon your view of I mean if I have something resting on the surface of the Earth, it's not accelerating. No way, no how. You will see that an accelerometer resting on the surface of the earth is being accelerated—by earth, through spacetime—and the strain gauge within it is “pushing down its its chair” at 1 g. You will see that Einstein has been right all this time.

Alternatively, from the point of view of Newtonian physics, the strain gauge inside an accelerometer resting on earth is being bent down (strained) by gravity—just like the snow-laden branches of a pine tree. We can look at this tree just as Newton did: where gravity is a downward force that pushes down on the branches of a stationary tree. Or we look at the tree just as Einstein did: where earth’s surface and the tree are accelerating upwards through spacetime, causing the tree branches to strain towards the center of the earth. From either point of view, the effect is the same: accelerometers respond equally to gravity and inertial acceleration. That’s why they really and truly output a +1 g signal when stationary.

This is the best explanation I can give. If you, Wolfkeeper, still disagree, then someone else will have to give it a try. Greg L (talk)

No, your interpretation of what is happening is incorrect. If you mount the accelerometer in the nose of a rocket that is pulling 1.01g, and it's 1 foot above the surface of the Earth, then it reads 1.01g. But it will gradually gain speed, and leave the Earth. After it has left the Earth, if the rocket is providing the same acceleration throughout (in other words the thrust is kept a constant multiple of the mass of the rocket), the accelerometer will still read exactly 1.01g, but the gravity has varied. This shows again that accelerometers are completely insensitive to gravity. This is precisely the same argument that Einstein advanced when developing the Equivalence Principle, he specifically talked about rockets, and it is related to why the rocket guys get this right, but most others do not. Rocket guys have to understand this stuff precisely, because if they don't their rockets crash; see Pendulum rocket fallacy for example- it's highly related.

Your argument that it is gravity that causes the accelerometer's mass to strain downwards is indirectly true in a sense, in that particular case, because gravity causes the acceleration that is reacted against, but in general it is not.

Even in Newtonian mechanics it's wrong. Newton's gravity pulls everything with the same acceleration, there's no distortion of the spring due to gravity, it's all due to external forces acting on the accelerometer; gravity can't do that.

These guys also get it pretty right (I know it's not a reliable source, but I'm just trying to show I'm not out to lunch here).[9]- (User) Wolfkeeper (Talk) 20:42, 19 January 2009 (UTC)[reply]

Fascinating, and I think I see where you are coming from here. This reminds me of past debates at lift (force). I think we need to keep things (relatively) simple on this article, and we need to stay close to the sources. If there is a decent source which uses this explanation then it could go in the article. But let's not go into arcane levels of complexity here. It seems to me (my opinion, and I did university Physics, albeit quite a while ago), is that the acceleration experienced is always a vector sum of gravitational and acceleration forces, and that GR states that the two are indistinguishable in their effects. If we can agree on these principles (and I hope we can), and they can be referenced, then that is what the article should say. Make sense? --John (talk) 20:55, 19 January 2009 (UTC)[reply]

The acceleration experienced is different from the overall acceleration. That's because you can't feel gravity any more than accelerometers can. Einstein commented on that specifically, he told a story of a painter that fell off a roof- he felt weightless as he fell: Zero-g.- (User) Wolfkeeper (Talk) 22:11, 19 January 2009 (UTC)[reply]

• Huhm. Ok, Wolfkeeper, I had to think for a moment there. If you de-tune the rocket’s engine 1%, then the accelerometer will read 1.00 g and the rocket goes nowhere. You will have to do a thought experiment now, and imagine moving the rocket by hand into space (or imagine the earth disappearing). In either case, the accelerometer continues to read 1 g. It’s just that gravitational acceleration (and no inertial acceleration), has been replaced by 1 g of inertial acceleration and zero g of gravitational acceleration. If you do the same for 1.01 g, as in your above post, then you will see the same effect: as the earth slowly recedes away and its gravity degreases, the rate of change in the velocity of the spaceship with respect to the earth (inertial acceleration) increases. This is certainly the behavior one would hope of a rocket, isn’t it(?): if you could instantly put a massive object like earth behind the rocket, then its rate of change in velocity with respect to the earth will instantly and substantially decrease due to all that gravity. Yet, an on-board accelerometer will remain absolutely unchanged. Keen, huh?

  As the article now says, “The connection between inertial and gravitational acceleration is profound. Albert Einstein showed in his 1916 paper on general theory of relativity that gravitational and inertial accelerations are identical and indistinguishable” and “Accelerometers respond equally to gravity and inertial acceleration.” Greg L (talk) 21:10, 19 January 2009 (UTC)[reply]

But if you have the vehicle hovering and you turn off the engine, the accelerometer immediately zeros, it doesn't remain at 1g. Again, the accelerometer isn't reading gravity, it's reading the acceleration due to the engine. And I completely agree that the gravity accelerates the vehicle downwards, but it does it in a way that doesn't affect g-force/accelerometers.- (User) Wolfkeeper (Talk) 21:31, 19 January 2009 (UTC)[reply]

• But if you have the vehicle hovering and you turn off the engine, the accelerometer immediately zeros, it doesn't remain at 1g. That is a correct observation. Then you write Again, the accelerometer isn't reading gravity… But wrong conclusion. All I can suggest is that you carefully read the article and what John and I are writing here. Try also getting your hands on an iPhone; you can get g-reading software for it. Gotta go. Greg L (talk) 21:37, 19 January 2009 (UTC)[reply]

Your argument continues only to be nonsensical. Additionally, the article where you even mention this doesn't attempt to explain this, nor is it referenced.- (User) Wolfkeeper (Talk) 22:17, 19 January 2009 (UTC)[reply]

According to the equivalence principle article what Einstein actually said was:

"we [...] assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system." (Einstein 1907)

The 'reference system' in this context is a frame marking the origin and x,y,z axes and a clock attached to it. He's saying that gravitational fields are equivalent to that frame accelerating away from you- not you accelerating. That's also why accelerometers can't measure gravity- they're not moving according to Einstein- the frame of reference is.- (User) Wolfkeeper (Talk) 22:22, 19 January 2009 (UTC)[reply]

Not nonsensical, but perhaps over-complicated. Einstein is good enough for me on this article. Detailed discussion like this may belong more properly on acceleration or General Relativity. Again, we should stay close to what the sources say on this article. --John (talk) 22:59, 19 January 2009 (UTC)[reply]

Not if they're actually wrong, we need reliable sources. I'm not going to remove that flag if you insist on 'simplifying' by allowing incorrect facts into the article. That's not simplifying. Einstein also said that 'everything should be as simple as possible, and no simpler' ;-) I'm probably going to have to cruise over to the physics groups in the wiki and get them to look at this, they may have access to copies of Taylor's Gravitation.- (User) Wolfkeeper (Talk) 23:15, 19 January 2009 (UTC)[reply]

(outdent) Once again, Wolfkeeper, you accurately quote facts, and draw incorrect inferences. Exactly; when spacetime is accelerating towards the center of the earth, that utterly annoying propensity for humans to stubbornly stand on the earth—rather than fall down a deep hole in the ground so we can stay with spacetime—causes us to accelerate upwards relative to spacetime. The rush of spacetime at us acts like a downwards force of gravity and affects everything that resists its motion. Even massless light is affected (which shows just how profound Einstein’s thinking was).

I truly think you’ve got an image that is locked in your mind as tenaciously as Greenpeace protesters when chained to the fences of a furrier. You really should see for yourself how accelerometers work. I strongly suggest you round up anyone’s iPhone and install the free (iTunes link) G‑meter application. You might also install the $8.99 (iTunes link) gMeter. The latter is nice. I own it. It allows you to calculate 0–60 times and quarter-mile times, horsepower, etc. But the former one, G‑meter, simultaneously shows you three g read-out dial faces—one for each of the iPhone’s three axis. Please do as I suggest; you will see for yourself that accelerometers respond to gravity and inertial acceleration alike. This will save us all here a metric butt-load of time.

Please also directly respond to John’s 18:40, 19 January 2009 and 20:55, 19 January 2009 posts. He’s not asking too much. Greg L (talk) 23:17, 19 January 2009 (UTC)[reply]

Greg, I am sorry if you feel I am asking too much; or was there a missing "not" in there? Wolfkeeper, I like the idea of bringing in others' views. Per Einstein as you quote him, I agree we need to write this in the simplest possible way without being misleading. However, I'd point out that if it is just one editor dissenting, it isn't fair to hold the article hostage with a disputed tag. Some reliable sources for your interpretation of Einstein and acceleration would be good because it differs from mine (and Greg's). I'm sure that if we stay with the sources (and everything I've ever read supports the view that gravitation and acceleration are indistinguishable), we can come up with a compromise version that will satisfy everyone. --John (talk) 23:26, 19 January 2009 (UTC)[reply]

• Oops. Damn. Missing “not”. Now corrected. Greg L (talk) 23:29, 19 January 2009 (UTC)[reply]
  • Thanks! I've raised this at Wikipedia talk:WikiProject Physics so maybe somebody there will come along and help us. --John (talk) 23:40, 19 January 2009 (UTC)[reply]

• I note that our Accelerometer article begins with this line: An accelerometer is a device for measuring acceleration and gravity induced reaction forces. I checked Honeywell’s FAQ page but this issue is so profoundly basic that they don’t address it. Why are we discussing this any further? This is basic logic and physics. Further, anyone who has spent five minutes with an accelerometer can see that it responds to both inertial and gravitational acceleration and hasn’t a clue how to distinguish between the two. Wikipedia’s processes don’t effectively deal with circumstances like this. Allowing a single editor to junk up an article with {disputed} tags after a good handful of editors with strong physics and science backgrounds believe it is correct frankly seems absurd to me. Greg L (talk) 00:57, 20 January 2009 (UTC)[reply]

Well, I've asked for a couple of the relativity task force people that have edited recently to join us. I'm very sure they'll back me up, although I have no personal connection to them, and I'm hoping they can find a good reference as well.- (User) Wolfkeeper (Talk) 02:49, 20 January 2009 (UTC)[reply]

Ah, I've just found a pretty good reference "Introduction to Space Dynamics by William Tyrell Thomson (1986)". It's a fairly widely used textbook.

In the context of section 6.10's an inertial navigation system which has 3 gyros employed to produce a angularly stable platform containing 3 axis accelerometers, Section 6.11 begins:

"The accelerometers mounted on the vehicle measure only the non Gravitational force F_ng acting on the vehicle, and therefore one must add to it the gravitational force F_g in order to determine the total force which determines the acceleration of the vehicle, F_ng + F_g = m a_y... The gravitational acceleration a_g, which depends only on the position is computed and added to the output of the accelerometers to give the vehicle acceleration a_v"- (User) Wolfkeeper (Talk) 02:49, 20 January 2009 (UTC)[reply]

I think that's clear, as I stated, in general, accelerometers don't measure gravitational acceleration/force otherwise they wouldn't need to add on an estimate for it to the output from the accelerometers for this system.- (User) Wolfkeeper (Talk) 02:49, 20 January 2009 (UTC)[reply]

Also, the accelerometer article says it measures gravitational reaction forces (sic). It doesn't say it measures gravitational accelerations, only the reaction to them; but that doesn't always happen.- (User) Wolfkeeper (Talk) 03:08, 20 January 2009 (UTC)[reply]

Oh, wait. I see what's wrong. Has your 3-axis accelerometer got 3 axis gyros in it or something as well? They're probably using a computer to deal with this issue, essentially making an inertial navigation system. You can't make assumptions based on how such a system behaves and then try to extend it to accelerometers and g-force. And that's a problem as well, you're using OR to write the article.- (User) Wolfkeeper (Talk) 03:08, 20 January 2009 (UTC)[reply]

I agree with Wolfkeeper and think that the article should state that accelerometers do not measure gravity's acceleration. It's true that within General Relativity's framework gravity is an inertial force (like centrifugal force and coriolis force), but that seems to be an unnecessary level of complication for that article. I'm in favor of keeping it simple enough that the average reader will be able to understand. Dauto (talk) 03:17, 20 January 2009 (UTC)[reply]

So how does the accelerometer "know" not to measure gravity, if the two forces are indistinguishable? I agree we should try and avoid over-complicating this. I came into this understanding the area perfectly and am now rather confused. Have I been fundamentally misunderstanding one of the great works of the 20th century all this time? --John (talk) 05:28, 20 January 2009 (UTC)[reply]

It literally can be considered to be as simple as just that all parts of the accelerometer accelerate at the same rate under gravity at all times, giving zero reading, and then you add on the effect of other accelerations linearly. Einstein has a cute explanation for why the whole accelerometer go at the same acceleration due to gravity, but it comes to the same thing really as Newton for our purposes. The only time you get a reading from an accelerometer is if there's an external force acting on the outside casing of the accelerometer and then the test mass moves on its spring. That causes a relative displacement between the casing and the test mass and causes a readout.

When it's resting on the ground, the weight of the accelerometer itself pushes on the ground and the ground pushes back on it (equal and opposite force) and that external force from the ground causes an acceleration on the accelerometer that makes a strain on the spring and that triggers a readout. That's also why the acceleration is registered as upwards. If you know it's just resting on the ground and not moving you can use it to infer what the acceleration due to gravity because it's equal and opposite.- (User) Wolfkeeper (Talk) 06:08, 20 January 2009 (UTC)[reply]

• Why are editors coming here to say that “accelerometers don’t measure gravity” when that’s the first thing they do out of the box? The only accelerometer that doesn’t respond to gravity is a broken one that can’t respond to anything. Why did I have to write that? This is absurd. Greg L (talk) 05:45, 20 January 2009 (UTC)[reply]

If you open it on a plane, it doesn't measure gravity, it measures the g-force of the plane. You actually can't measure gravity while you're on the plane, all you're measuring is the instantaneous g-force due to the aircraft's lift, but the accelerometer isn't broken.- (User) Wolfkeeper (Talk) 06:08, 20 January 2009 (UTC)[reply]

Thanks for explaining what you meant, Wolfkeeper. I think what you are saying could maybe be used to explain why an accelerometer at rest (or in constant motion) registers 1 g upwards, the opposite of the direction of gravitational force. I don't think there is as much difference as you think between your explanation and Greg's. I really don't think this article is the place to get into these complex explanations, because as we see here in talk, there are many different conceptual models and we would then have to have several different models in the article. It's easier to keep this simple I think. --John (talk) 06:19, 20 January 2009 (UTC)[reply]

• Yes, Wolfkeeper. I completely agree where you wrote When it's resting on the ground, the weight of the accelerometer itself pushes on the ground and the ground pushes back on it (equal and opposite force) and that external force from the ground causes an acceleration on the accelerometer that makes a strain on the spring and that triggers a readout. That's also why the acceleration is registered as upwards. Greg L (talk) 06:26, 20 January 2009 (UTC)[reply]

Yes, but you can't go further than that because it's deceptive to say an accelerometer measures the gravitational acceleration, only that it can be used in some (albeit common) circumstances to determine that. I mean, you can use a barometer to measure the height of a tower by measuring the difference in air pressure, but that doesn't mean that it's a ruler, and there wouldn't be an article that read 'a barometer is a way of measuring air pressures and the heights of buildings' to have an only slightly forced example.- (User) Wolfkeeper (Talk) 07:00, 20 January 2009 (UTC)[reply]

Again though, we are going too far into the philosophy of science here. An accelerometer measures (can measure) gravitational force, which is indistinguishable from acceleration g. Your barometer example is a nice one; an aircraft's or a mountaineer's altimeter is exactly that, a specialized barometer calibrated for height, though not of buildings. I would agree that it isn't common for an accelerometer to be purposely used to measure gravitation as it is pretty invariant. But an accelerometer is surely always measuring the vector sum of gravity and acceleration, isn't it? Anyway, I feel we are in danger of arguing about angels dancing on pins here. Wolfkeeper, can you suggest what wording you would like to see? --John (talk) 07:28, 20 January 2009 (UTC)[reply]

No, it doesn't add the vector sum of gravity and anything, since gravity always reads zero. And yes, a barometer can be made to make, or operated as, one kind of altimeter, but they're not logically or necessarily precisely the same thing. Similarly an accelerometer is not necessarily a gravimeter but they can often be used to make one, not necessarily a good one. An accelerometer always measures g-force. G-force is always and only a property of the external forces, not the 'internal', inertial forces like gravity. Accelerometers read zero, for all inertial forces, every time.- (User) Wolfkeeper (Talk) 12:50, 20 January 2009 (UTC)[reply]

1) What is your source for this assertion? ("Accelerometers read zero, for all inertial forces, every time") It seems to contradict what you said above when you said "it's deceptive to say an accelerometer measures the gravitational acceleration, only that it can be used in some (albeit common) circumstances to determine that"

2) Why is it so important to put this in the article, as opposed to say in proper acceleration?

3) An aneroid barometer is logically and philosophically precisely the same thing as an altimeter. It is just calibrated differently.

4) I ask again, what wording would you like to see in the article, and with what sources? --John (talk) 14:25, 20 January 2009 (UTC)[reply]

1) it's widely known that gravitational accelerational in GR is an inertial acceleration. Inertial accelerations generate no g-force. Accelerometers measure g-force. 2) so: "don't bother me with facts, this is only the wikipedia!" is your attitude? 3) No, one way of constructing one type of altimeter is to calibrate a barometer for that purpose. It's one application of a barometer. If you don't believe me, by all means call for merge of the articles in the wikipedia. One application of a accelerometer is as a gravimeter. 4) just state that they measure non inertial accelerations, and point out that gravity is an inertial acceleration. - (User) Wolfkeeper (Talk) 14:54, 20 January 2009 (UTC)[reply]

• I don’t understand why you keep on writing stuff like since gravity always reads zero. The only time an accelerometer reads zero in a gravitational field is when it is falling. If an accelerometer isn’t accelerating upwards or downwards with respect to earth’s surface, it reads 1 g upwards due to the force of gravity. You obviously don’t believe that what the article is now saying is correct. All I can say is that it is clear enough for the rest of us here. Greg L (talk) 16:53, 20 January 2009 (UTC)[reply]

Why is there a dispute at all?

Accelerometers measure proper acceleration. The proper acceleration of a body is its acceleration minus the gravitational field at the place it is. (For example, my proper acceleration right now is approximately 9.8 m/s upwards.) According to general relativity, both the acceleration of a body and the gravitational field on it depend on the frame of reference used, but their difference, the proper acceleration, doesn't. (For example, in the geocentric reference frame, I am stationary and subject to a downwards gravitational field of approximately 9.8 m/s; whereas in the free-falling frame, there is no gravitational field (by definition), but I'm accelerating upwards at approximately 9.8 m/s.)

Hence, the question about whether the "1 g" an accelerometer placed on a table is an acceleration or a gravitational field is meaningless unless we specify a frame of reference. As for me, I don't like using a frame of reference in which Italy and New Zealand are accelerating away from each other but their distance isn't changing, but YMMV, and according to general relativity there is no rationale for my dislike.

What part of this doesn't everybody agree with? -- Army1987 – Deeds, not words. 17:24, 20 January 2009 (UTC)[reply]

Sounds good to me, Army 1987. For the eleventy-seventh time though, this article should not be the place for a detailed discussion of general relativity or proper acceleration. They have their own articles which we can link to and summarize briefly. Neither should it deal with competing conceptual models of "why" an accelerometer reads a particular value. My physics is a little rusty but I do recall that according to GR there is no way to distinguish gravitational force from acceleration force, which makes it improbable that an accelerometer can accomplish this. I like the proposal you are making. --John (talk) 20:31, 20 January 2009 (UTC)[reply]

• No Army. Accelerometers do not measure only “proper acceleration”. Where in the world did you get that idea? If they did, they wouldn’t read 1 g when stationary, would they?

  As for Hence, the question about whether the "1 g" an accelerometer placed on a table is an acceleration or a gravitational field is meaningless unless we specify a frame of reference. I am baffled why you would write such a thing. The answer is simple: relative to where the accelerometer is sitting. Since that is the common-sense way of looking at it, it need not be specified that we don’t mean relative to someone on the other side of the world.

  Single-axis accelerometers can’t distinguish between off-angle orientations, gravity, inertial accelerations, or any combination of the three. They know only acceleration along a vector and they respond equally to gravity and proper acceleration.

  There is simply no way of properly denying this unless you deny that a single-axis accelerometer reads 1 g when oriented vertically and 0 g oriented horizontally. And off course I am talking about when it is sitting in your frame of reference—not Mars or something weird. If you agree that this observation is true (1 g when vertical, 0 g when horizontal), then you must agree that accelerometers respond to gravity. This is just so basic. Greg L (talk) 06:29, 21 January 2009 (UTC)[reply]

Unfortunately, you are demonstrating only too well that it is not so basic. A single axis accelerometer does not read 1g downwards in that situation in a gravitational field. It is therefore not reading gravity which is a downward acceleration.- (User) Wolfkeeper (Talk) 06:38, 21 January 2009 (UTC)[reply]

So it's reading the reaction to gravity then? The upward acceleration? --John (talk) 08:10, 21 January 2009 (UTC)[reply]

• Yes. It is reacting to the force of gravity. In the plain ol’ common-sense way where you open up the box and turn it on and it says “1 g” and you can’t make the signal go away unless you jump off a roof. The issue is about writing crap like “an accelerometer responds to non-gravity accelerations.” This is what Wolfkeeper keeps on trying to do. Greg L (talk) 08:34, 21 January 2009 (UTC)[reply]

You're precisely correct John, it's reading the reaction to gravity- reaction in the Newtonian action and reaction sense. It can indirectly read gravity, but never, ever directly. Note that Greg_L when apparently he agrees above, is actually not saying the same as you. He doesn't understand it.- (User) Wolfkeeper (Talk) 16:19, 21 January 2009 (UTC)[reply]

Pedant-point: this isn't an action-reaction pair, which is always a mutual interaction between two objects. (So, the reaction to the gravitational force on the device is the reactive gravitational force on the earth.) --Starwed (talk) 05:31, 22 January 2009 (UTC)[reply]

Proper acceleration is essentially (if you're not going near the speed of light) acceleration minus the gravitational field. So an accelerometer on a table, in the frame of reference of the table, is subject to zero acceleration and to a gravitational field of g downwards, so the proper acceleration is g upwards. BTW, acceleration relative to where the accelerometer is sitting is zero by definition (or did you mean something else by sitting?), so in that particular frame what the accelerometer measures is just the negative of the gravitational field (or the reaction to the gravity, as you prefer to call it). We're not disagreeing about the physical phenomena, just about how to call things. -- Army1987 – Deeds, not words. 14:51, 21 January 2009 (UTC)[reply]

The thing is, if we use the wrong words in the article it can actually give people the impression they understand it when they don't. Of course we can confuse people by being too technical also, and I don't want to do that either. Greg_L is probably a really good example of what happens when people just don't quite get it.- (User) Wolfkeeper (Talk) 16:19, 21 January 2009 (UTC)[reply]

I hate these mile-long threads. Surely this dispute is merely about terminology. I think everybody here agrees on how an accelerometer will behave in every actual physical situation. An accelerometer in freefall will read zero (or close to zero—it might notice tidal acceleration). An accelerometer sitting on a table will read 9.8 m/s² vertically. An accelerometer measures (approximately, in ordinary circumstances) the magnitude of its own deviation from gravitational freefall. So, does an accelerometer measure gravitational acceleration? On the one hand the readout uses gravitational freefall as a baseline, so no. On the other hand an accelerometer can be used to measure the so called local acceleration of gravity at any point on the Earth by setting it on a table and looking at the readout, so yes. These are not contradictory answers, they're answers to two different questions that happen to be expressible with the same sequence of English words. I think the solution is simple: don't use that sequence of English words, or any other sequence that can be interpreted both ways.

I think it's also worth pointing out that accelerometers don't really measure proper acceleration, or any externally meaningful quantity, as such. A froglevved mechanical accelerometer will read zero, even though an identical accelerometer sitting right next to it on a table, and clearly at relative rest, will read 9.8 m/s². That said, you could design a sophisticated accelerometer that could compensate for all other influences by using a variety of differently-responding materials (like those amazing mechanical clocks of John Harrison's) but you can never avoid the freefall reference (unless you're allowed to use an external reference body like GPS), so in that sense there is something deep going on here. -- BenRG (talk) 15:41, 21 January 2009 (UTC)[reply]

I really agree with you, I've hated every minute of this talk page. But it's not really terminology, we're not arguing colour or color, it's more backup (reversing) and backup (saving stuff). The frog levitation only applies to water, and a few other materials, if you made an accelerometer out of non diamagnetic material it would actually work perfectly, and wouldn't levitate. Hmm, come to think of it, if you were to accelerate the huge magnet, the frog would make a perfectly fine accelerometer already ;-)- (User) Wolfkeeper (Talk) 16:19, 21 January 2009 (UTC)[reply]

I believe that proper acceleration is completely the correct term though, even if you're going near the speed of light.- (User) Wolfkeeper (Talk) 16:19, 21 January 2009 (UTC)[reply]

The Associated Press observes this practice world-wide regarding when to capitalize “earth”. This is from Grammar.ccc.comment.edu:

• [Do capitalize] Names of celestial bodies: Mars, Saturn, the Milky Way. Do not, howver, capitalize earth, moon, sun, except when those names appear in a context in which other (capitalized) celestial bodies are mentioned. "I like it here on earth," but "It is further from Earth to Mars than it is from Mercury to the Sun.

I always wrestled with this issue. I see now that the practice is nuanced. Greg L (talk) 19:31, 19 January 2009 (UTC)[reply]

Hmm. But our article on Earth consistently uses capital E, and it is featured. --John (talk) 20:13, 19 January 2009 (UTC)[reply]

• <tone of being facetious>You mean, a Wikipedia article isn’t correct?!?</tone of being facetious>. Our own WP:MOS has it correct at #Celestial_bodies. It’s a grammar & punctuation thing; not everyone gets it right, but professional writers (who read their manuals of style) apparently do. Like I said, I just learned this myself. Greg L (talk) 20:50, 19 January 2009 (UTC)[reply]

• The MOS has "capitalized ... in an astronomical context when referring to specific celestial bodies (our Solar System, Sun, Earth, and Moon): The Moon orbits the Earth, but Io is a moon of Jupiter." It therefore seems to me that Earth should be capitalized on this article. --John (talk) 20:59, 19 January 2009 (UTC)[reply]

• The MOS gives these examples: The sun was peeking over the mountain top. And The Moon orbits the Earth, but Io is a moon of Jupiter. This is consistent with what the above referenced grammar site says: One writes: I like it here on earth and also writes "It is further from Earth to Mars than it is from Mercury to the Sun. Both sources are consistent with each other as they both conform to this rule of punctuation: Do not, howver, capitalize earth, moon, sun, except when those names appear in a context in which other (capitalized) celestial bodies are mentioned. The MOS version of this principle is as follows:

Sun, earth, and moon are not capitalized when used generally: The sun was peeking over the mountain top. They are proper nouns and capitalized when personified: Sol Invictus ("Unconquered Sun") was the Roman sun god. and in an astronomical context when referring to specific celestial bodies (our Solar System, Sun, Earth, and Moon): The Moon orbits the Earth, but Io is a moon of Jupiter.

The g-force article doesn’t speak of any capitalized references to other celestial bodies (the Earth, Moon, and Mars); it just talks about issues like “earth’s surface”. That’s why it’s properly done lowercase. Greg L (talk) 21:18, 19 January 2009 (UTC)[reply]

I don't have a problem with it being lower case on this article. Maybe a post at Talk:Earth is in order though? --John (talk) 23:00, 19 January 2009 (UTC)[reply]

Done. --John (talk) 23:36, 19 January 2009 (UTC)[reply]

• Articles like Earth are frequented by a diverse lot. When my middle daughter was two years old, I was sawing some wood out back in the scrub brush portion of my property just off the lawn. I heard a noise of discontent from her and looked up. She had literally stirred up a hornets’ nest and they were swarming around her. Without thinking, I bolted towards her (wondering what the hell I was going to do when I got there). I had about 1.5 seconds to figure it out. Simple solution: I snared her arm like a steaming train catching a mail bag with its hook. I slowed down a bit when I reached the lawn, lowered her down and dragged her along on the grass as I slowly rolled her to scrape off any hornets. I stood her up and checked her out. She wasn’t crying. She didn’t even seem bothered. She didn’t have a sting on her.

  Odd; your suggestion that someone go to Talk:Earth with this observation about capitalization just now reminded me of that incident. Busy chopping wood here. I’m glad you did. Greg L (talk) 23:43, 19 January 2009 (UTC)[reply]

We need to clarify that g-force usually refers to a sustained acceleration. Shock and Impact are used to describe short term transient accelerations. All can be reported in multiples of g. This should go in the introductory section. Rlsheehan (talk) 02:47, 20 January 2009 (UTC)[reply]

Yes. I can bring sourcing to this. --John (talk) 03:14, 20 January 2009 (UTC)[reply]

• Woa, woa. How’s that?? G-force is used primarily for sustained accelerations only if you are in the business of sustained accelerations. G-force is used all the time in vibration testing and other transient phenomenon—including shock. I designed industrial instrumentation and worked with UL and CSA. Shaker tables can be found big & small and operate a very wide range of frequencies depending upon the need. Nothing needs to be clarified regarding “sustained acceleration”; that notion is completely incorrect. There is no magic time period in industry over which g-force becomes less common. It might only seem that way to the general public that is primarily exposed to g-forces when watching Red Bull air races. If anything, I need to add a few line items to the table to give some lip service to vibrational g-forces. Greg L (talk) 05:35, 20 January 2009 (UTC)[reply]

• Nearly all of the current article deals with sustained g-forces though. We would need (I think) to have a short section with a sourced discussion on transient versus sustained, with links out to shock (mechanics) and impact force where most of the material relating to short-acting g would best be placed. There's a bunch of stuff in that air crash book I could bring to this. --John (talk) 05:46, 20 January 2009 (UTC)[reply]

• And also jerk (physics). --John (talk) 05:49, 20 January 2009 (UTC)[reply]

• Agreed. Something about vibration testing would be good. Vibration testing is really common and needs fair play here. Underwriters Laboratories and IEC (I’ve redesigned American equipment and certified it to IEC for sales overseas) both embody standard industrial practices in their standards. So both would be good sources for gathering up background upon which to base that section. Do you want me to do this or do you want to, John? I wouldn’t mind. The only reason I write stuff is because I want to brush up on it and understand in serious depth.

  And, yes, something about jerk. If one didn’t know the term, you’d never find it. This is a great place to mention it. Greg L (talk) 05:54, 20 January 2009 (UTC)[reply]

• (outdent). Do you want to tackle jerk, John? I can keep myself real busy giving a proper treatment to transient. It will also take several days for me to formulate what I want to write in my mind. Greg L (talk) 05:58, 20 January 2009 (UTC)[reply]

• Feel free to have a pop at it. I'm off to bed now. --John (talk) 06:30, 20 January 2009 (UTC)[reply]

What “air crash book” are you referring to, John?

• • Beyond the Black Box: the Forensics of Airplane Crashes by George Bibel, John Hopkins University Press, 2008 (ISBN 0-8018-8631-7) A great book with an unusually detailed coverage of scientific principles. Loads of good stuff on metal fatigue and g-loads in crashes. --John (talk) 06:22, 20 January 2009 (UTC)[reply]

• Books in the hands of Wikipedia authors. Mmmmm. Greg L (talk) 06:28, 20 January 2009 (UTC)[reply]

• Books published by reputable publishing houses have an editorial process which makes them good reliable sources, at least in theory. I'm off to see what conceptual model Bibel uses to explain g. Maybe he can shed more light on the best way to explain it accessibly on this article. --John (talk) 07:34, 20 January 2009 (UTC)[reply]

Vibration, shock, jerk, and impact all have to do with the dynamic response of an item to input. Sustained loads are easier. I suggest that this article NOT address the short term loads and vibrations which involve dynamic response. Rlsheehan (talk) 14:58, 20 January 2009 (UTC)[reply]

• I don’t have a rocket up my butt to address vibration in depth. As you point out, it can be complex. However, the role of any encyclopedia is to educate readers with minimal confusion and ensure they are well prepared to absorb information in their studies elsewhere on the subject. We also properly and honestly use terminology and symbology so readers can be conversant with others experienced in the art. We could probably use something about vibration here that informs readers of sinusoidal g-forces without getting bogged down in the minutia of reactive harmonics and other unnecessary complexities. In the mean time, I’m intent on directly and succinctly addressing the issue of “force” and how it relates to acceleration and gravity and the way Newton understood forces. Greg L (talk) 16:45, 20 January 2009 (UTC)[reply]

The problem with this article is that it does not define its terms, and seems to be talking about a blend of different topics under the same heading. In what we think of as the real world, there is less-than-complete consensus as to what “gravity” is, and what the symbol “g” means. This article does little to clarify it. It seems to be discussing a mixture of:

• g, the quantity of gravitational acceleration, which varies from place to place.
• g, a unit of measurement which is used to measure gravitational acceleration.
• g_n, standard gravity which is the normal acceleration due to Earth's gravity - 9.806 65 m/s²
• g_I, ideal gravity on an isolated homogenous spherical nonrotating airless planet
• g_L, laboratory gravity, which is g_I corrected for rotation, spherical aberration, density variation, weather, etc. etc
• g_E, Einsteinian gravity, in which acceleration and gravity are equivalent, and which is zero in an orbiting spacecraft
• F_g, force of gravity: F_g = mg
• w, weight caused by Earth's gravity: w = F_g = mg
• F_a, force caused by acceleration: F_a = mg
• w_a, apparent weight caused by acceleration: w_a = F_a = ma
• F_c, centrifugal force, a fictitious force caused by rotation: F_c = mω²r
• w_c, apparent weight caused by centrifugal force: w_c = F_c = mω²r
• G_f, the ratio of apparent weight to real weight: G_f = ma/mg

The last, G_f, seems to be closest to the main topic, "g-force". If you substitute m (for mass) for mg (for weight), the units work out to be those of acceleration, which seems meaningful.RockyMtnGuy (talk) 01:23, 21 January 2009 (UTC)[reply]

• Per its abundant citations, it is discussing g, which has a magnitude equal to gn. Greg L (talk) 04:24, 21 January 2009 (UTC)[reply]
  • Although the others should perhaps be mentioned; not all as some are subsets of each other. --John (talk) 08:25, 21 January 2009 (UTC)[reply]

Wolfkeeper. With these edits, you keep on promoting the notion that accelerometers respond only to proper acceleration. This is absurd. To claim such a thing, you must provide an explanation for why an accelerometer will read 1 g when oriented upwards, and 0 g when oriented sideways. If you deny that this is true, then you deny an indisputable fact of the way accelerometers work. If you agree that this is the true behavior of accelerometers, you therefore are agreeing that they clearly respond to the acceleration of gravity.

It would also be nice if you didn’t ruin articles with links that look like this. Greg L (talk) 06:10, 21 January 2009 (UTC)[reply]

Sorry, but I removed uncited material, and inserted cited material that is referenceable to a WP:RELIABLE source. You can read the text at: [10]. Your claims of 'common sense' are OR.- (User) Wolfkeeper (Talk) 06:20, 21 January 2009 (UTC)[reply]

• What is wrong with you? You just cited a reference that proves my point and disproves yours. Didn’t you read it? It is talking about a nuance of its output signal. It reads as follows:

[An accelerometer] cannot distinguish between inertial acceleration [a-bar] and gravitational acceleration

Stop pushing this notion of yours. It is absurd and you just found a reference that speaks of accelerometers having no ability whatsoever to distinguish between proper (inertial) accleration and gravitational acceleration, which is what I’ve been saying all along (and what the article says). Greg L (talk) 06:37, 21 January 2009 (UTC)[reply]

You've taken it out of context and misread it as well.- (User) Wolfkeeper (Talk) 06:45, 21 January 2009 (UTC)[reply]

Look at the equation.- (User) Wolfkeeper (Talk) 06:45, 21 January 2009 (UTC)[reply]

• No. The statement:

[An accelerometer] cannot distinguish between inertial acceleration [a-bar] and gravitational acceleration

It goes on to talk about how to separate the inertial acceleration from the mix of inertial and gravitational signals by subtracting out the gravitational signal from known navigator position and attitude. It reads as follows

Hence, the accelerometer cannot by itself provide the determination of inertial acceleration required for navigational purposes. Therefore, to get the total acceleration vector, accelerometer triad outputs must be added to the gravitational acceleration vector, which is calculated from the known navigator position and attitude;

This is beyond absurd. You’ve never seen an accelerometer before in your life, have you? Greg L (talk) 06:51, 21 January 2009 (UTC)[reply]

Yeah, I have actually, thanks. Oh and I checked with somebody who is consulting for an aircraft manufacturer to build a gradient gravimeter, and he absolutely and completely confirmed it.- (User) Wolfkeeper (Talk) 06:54, 21 January 2009 (UTC)[reply]

The equation given in the book is f = a - g

where f,a,g are vectors. g is the acceleration due to gravity and points downwards (0,0,-9.8). a is the acceleration in the inertial frame, say (0,0,0), and f is the acceleration that the accelerometer gives f= (0,0,9.8)- (User) Wolfkeeper (Talk) 06:54, 21 January 2009 (UTC)[reply]

As it states, f does not read the acceleration due to gravity and you have to add it on to get the right answer. In the case of your accelerometer just sitting there on the table, you have to calculate and add on the downwards g to get the correct motion (in that case it's not moving.)- (User) Wolfkeeper (Talk) 06:59, 21 January 2009 (UTC)[reply]

• Apparently, every single bit of “[An accelerometer] cannot distinguish between inertial acceleration [a-bar] and gravitational acceleration” confuses you. Greg L (talk) 07:15, 21 January 2009 (UTC)[reply]

The only thing I don't understand is why you think it supports your position, when it clearly doesn't. I also don't understand why you though you could in any conscience cut it out of the full sentence which reads:

Unfortunately, an accelerometer measures the nongravitational specific force, output = f = a - g, and cannot distinguish between the inertial acceleration, a and the gravitational acceleration, g. Hence the accelerometer cannot by itself provide the determination of inertial acceleration required for navigational purposes. Therefore to get the total acceleration vector, accelerometer triad outputs must be added to the gravitational acceleration vector, which is calculated from the known navigator position and altitude a = output + g(r). Specific force is simply another word for acceleration, (specific means per unit mass, specific force is force per unit mass; f/m = a; and it actually says that specific force is acceleration a little further down). a is the acceleration relative to the rest mass of the Earth, and is what they're trying to calculate (it's an inertial navigator). It's very, very clear. And you're removing it purely because of your own OR. I mean does it ever occur to you that you're actually wrong. There was also the other two references I found: [11]"From a classical physics perspective, an accelerometer is a device that measures the acceleration due to all forces acting on the accelerometer case except gravity." and there was the astrodynamics text book I mentioned above. - (User) Wolfkeeper (Talk) 07:38, 21 January 2009 (UTC) I also today got an email from Henry Spencer who is a professional aerospace engineer, noted for being absolutely precise about every goddamn thing. There was also half a dozen others that said exactly the same thing in various phraseologies. All you've got is a bunch of OR, a rather severe misunderstanding of the physics involved and a revert button, and claims that playing with an accelerometer for a bit makes you an expert. Um. No.- (User) Wolfkeeper (Talk) 07:38, 21 January 2009 (UTC)[reply]

• Look up and what the letter writer wrote. How many times does it say it reads 1G when sitting on the ground? Lots, right? You fail to see what the above letter is saying. The same to for what the article says. The letter writer you quoted above isn’t cluing in on the fact that you question whether accelerometers respond to gravity. They are assuming you know this and are asking about sensing the *gravity itself*. They’re trying to answer an abstract issue of detecting the the gravitational field. And the letter writer is telling you that an accelerometer reads 1 g when it is stationary on the ground because the earth holds it up in gravity. The article makes all this clear to: it is the earth pushing the accelerometer upwards through spacetime that makes it read 1 g on the ground. The whole point of the book you are citing is talking about how difficult it is to tease out small inertial signals when there is the big gravitational signal. The key point you should have picked up on here is where it says “An accelerometer] cannot distinguish between inertial acceleration [a-bar] and gravitational acceleration”. This is almost verbatim to what the our article says. Accelerometers respond to both gravity and inertial accelerations and can’t tell the difference between the two. This is precisely as the book says. It is simply absurd to claim that accelerometers respond only to inertial acceleration and not to gravity. The entire above letter makes it clear that they respond very much to gravity when they are stationary. Greg L (talk) 08:11, 21 January 2009 (UTC)[reply]
  • Nice post. I wish you two could depersonalize this a bit; you are not really that far apart from each other but you have become entrenched. I know you've been in conflict for a while now, but if you could step away from the personalities for a moment. Language like "All you've got is a bunch of OR, a rather severe misunderstanding of the physics involved and a revert button" and "You’ve never seen an accelerometer before in your life, have you?" isn't helping us move forwards here. Per WP:EXPERT, our own personal qualifications and experience don't count for diddly here, and we must instead go to the sources. Blog postings aren't the best sources here, and we should stick to a brief description per the sources, and try to avoid getting too personal here. With all respect, --John (talk) 08:24, 21 January 2009 (UTC)[reply]
    • Look, basically, it won't take many seconds of anyone fairly educated in physics looking at the source I added and the article is going right back to my version. What I wrote isn't in any way debateable. I've asked User:SBHarris to look at it, he's a doctor but he knows a lot about physics and he's bloody smart. If he says I'm wrong, I'm wrong. I'm going to ask a few others as well.- (User) Wolfkeeper (Talk) 08:40, 21 January 2009 (UTC)[reply]
    • I've also called in User:Georgewilliamherbert he's an admin as well as an aerospace engineer, but I've asked him to comment in a non admin capacity.- (User) Wolfkeeper (Talk) 08:52, 21 January 2009 (UTC)[reply]

• Fine John, let’s go with the sources. He found one that says as follows:

[An accelerometer] cannot distinguish between inertial acceleration [a-bar] and gravitational acceleration.

From this he writes “an accelerometer which gives a measurement of an object's non-gravitational acceleration.” This is false. Further, even his above-quoted letter is chock full of “1G” due to the influence of gravity. The article properly says that “Accelerometers respond equally to gravity and inertial acceleration.” It is time to stop letting Wolfkeeper hold this article hostage with a {disputed} tag. Greg L (talk) 08:31, 21 January 2009 (UTC)[reply]

Simple issue: is the following paragraph correct?

An accelerometer measures acceleration in one or more axis. It responds to both gravitational and inertial acceleration. If you orient a stationary, single-axis accelerometer so its measuring axis is horizontal, its output will show zero gee. Yet, if you rotate the accelerometer 90° so its axis points upwards, it will read +1 g upwards even though still stationary. If you mount the accelerometer in an automobile with its axis aligned forward with the vehicle’s direction of travel, and drive down the road at a constant speed, it will read 0 g. Yet, if you hit the brakes, it will read about −0.9 g. Accelerometers respond equally to gravity and inertial acceleration.

You, Wolfkeeper, found a book that says as follows:

[An accelerometer] cannot distinguish between inertial acceleration [a-bar] and gravitational acceleration.

Let’s have you, Wolfkeeper, start off with real clear explanation of exactly what you think is wrong with the above paragraph. Greg L (talk) 08:51, 21 January 2009 (UTC)[reply]

I already have repeatedly, I'm not commenting further, it's for others to do so.- (User) Wolfkeeper (Talk) 08:54, 21 January 2009 (UTC)[reply]

• That’s fine. Here is the edit you’ve been repeatedly making. This is the crux of the issue: You’ve been saying here that accelerometers measure only inertial acceleration, not gravity-based acceleration. The question is: are you right about that? Greg L (talk) 09:20, 21 January 2009 (UTC)[reply]

• For the record, he is. Whenever you THINK you're measuring gravitational acceleration (strength of g-field) with an accelerometer, all you're really doing is measuring the force (ordinary mechanical force) needed to keep the accelerometer motionless in that field. But you can turn THAT mechanical force off and on, and the accelerometer will just measure it (or not) and though it all, it still won't measure the g-field, which could be anything (any value) though any of it. Is that simple enough for everybody? SBHarris 13:39, 21 January 2009 (UTC)[reply]

• Hmm: Check this. This is from MEMSIC.com. They make sensors for “consumer, automotive, medical or industrial product applications”. It is titled ACCELEROMETER PRIMER. And it begins with this:

Accelerometers are used to convert an acceleration from gravity or motion into an electrical signal.

(My emphasis). I really do hope this is clear enough. Greg L (talk) 09:08, 21 January 2009 (UTC)[reply]

Ahhhhhh (thud) - the sound of George's head hitting the keyboard again and again

Look... This was slightly lame when the discussion started a couple of days ago on the arocket mailing list, and isn't helping here. The terminology is not sufficiently precisely consistent between different branches of physics, and between different branches of engineering, and between physics and engineering. It's possible to use reliable sources to pedantically prove that 1 = -1 quite easily on this topic, using sources that disagree on precise definitions or are internally not rigorously consistent. That exercise is trivial and not helpful.

It is not proper to take articles off into long pedantic fights. Wikipedia articles are part of a general encyclopedia. They have to explain things so that normal people have some chance of understanding. They most particularly must not cause people to come away from the article confused or with an incorrect understanding.

It is particularly important for editors to be aware of this on topics which are, even for experts, badly or imprecisely defined, and particularly again for topics popular or widespread enough that a lot of people are likely to come read it. We have in our hands the power to go off in any arbitrary direction on any set of reliable source information and in doing so commit evil upon the intellectual development of the world writ large.

In clear terms: There is no difference between a gravitational and an inertial acceleration, per Einstein. We're sitting in a 1-G static gravitational field. There's a force exerted by the ground, floor, and chair which counter the gravitational acceleration force downwards.

If we try and get too pedantic on this it will nuke the conversation right out of people's ability to follow, which is a sufficiently fundamental error that I call foul and ask for time out.

[ I particularly object that this came up on a topic where I persistently for no clear reason want to misspell accelleration with an extra l, which my brain keeps insisting should be there despite clear evidence to the contrarry... ]

Georgewilliamherbert (talk) 09:18, 21 January 2009 (UTC)[reply]

• Thank you, Georgewilliamherbert. Where you write, In clear terms: There is no difference between a gravitational and an inertial acceleration, per Einstein. We're sitting in a 1-G static gravitational field, that’s what I’ve said over and over and over here on this talk page. That’s what the article says. But as the principle applies to accelerometers, Wolfkeeper has been saying it is WP:OR to say that “Accelerometers respond equally to gravity and inertial acceleration.” Quite frustrating. I’m sorry you got dragged into this. Greg L (talk) 09:24, 21 January 2009 (UTC)[reply]

I'm really sorry to drag you in George, and I agree with not making it too difficult and everything, but I don't think I was, and we're talking about g-force, which is always the non gravity bit. You can't in any case ever feel a gravitational acceleration, and the reverted article starts with stating you can. I have no problem at all with writing this as clearly as humanly possible, but I don't see that we can't write things that are simply wrong.- (User) Wolfkeeper (Talk) 09:31, 21 January 2009 (UTC)[reply]

I hope you don't think I picked and chose my sources either George, I just looked for the best quality source I could find, and even this one is hard to read; if I genuinely had found any real discrepancies I would never have gone with this source, I would have added multiple references to different POVs in some way.- (User) Wolfkeeper (Talk) 09:36, 21 January 2009 (UTC)[reply]

• What is your mental block here? George was clear. And yet, here you are writing You can't in any case ever feel a gravitational acceleration. It doesn’t matter whether or not you can feel it; I can. It makes my apple fall to the ground and the food stay on the bottom of my stomach. It makes snow-laden branches on trees sag down. When accelerometers are sitting around on earth, like pretty much anything else you see, including yourself, they do feel gravity—exactly like tree branches. And accelerometers send out a 1 g signal testifying to the fact that they’re being exposed to the force of gravity; they all do. Get that into your head please. Accelerometers detect gravity. They send a signal saying they do. When engineers (which I happen to be) do important work with accelerometers in inertial navigation units, they have to figure out clever ways to get that damned gravity signal out of the way. If you turn a single-axis accelerometer sideways, the gravity signal disappears. Moreover, the simple fact is that the above paragraph is true. Accelerometers respond to both gravitational and inertial acceleration and cannot differentiate between the two, just as George said. NOW STOP EDITWARRING please. Greg L (talk) 09:46, 21 January 2009 (UTC)[reply]

• You're not feeling gravity, either. All you feel is mechanical pressure from an electromagnetic force^{[citation needed]}. Food stays on the botton of your stomach because your stomach pushes up on it. It would do the same if you were in a rocket, with no gravitational field whatever. And your accelerometer would not know the difference, either. SBHarris 13:42, 21 January 2009 (UTC)[reply]

• No, SBHarris, gravity is not an “electromagnetic force” by any stretch of the imagination. Please cite where you got that bit of info. Nor is the effect of gravity a “pressure” in any fashion. Sorry. Greg L (talk) 18:43, 21 January 2009 (UTC)[reply]

• Gravity is not electromagnetic, true, but that is okay, because you're not feeling gravity. You never feel gravity. You can only feel electromagnetic stress (mechanical pushes). The same with an accelerometer. When nothing but gravity acts on you, you feel nothing. You're floating at what feels exactly like being under no-force. Accelerometer reads "zero."

  Stand on a table out in space, being boosted underneath by a rocket at 1 gee. You're not feeling gravity (there isn't any), you're feeling mechanical stress on you body transmitted though your feet. That's all your body's resistance to changing v; or inertial force. It's electromagnetic. Ramp it up and it will squash you. Hover that platform over the Earth, and you still do not feel gravity. All you feel is 1-gee inertial force. Turn the rocket off and land and you still do not feel gravity; again just the inertial force of the terrain pushing up on your shoes, keeping your body from following its natural geodesic path though spacetime, by applying an EM force to your feet (which transmits up to the food in your stomach). In all cases, the accelerometer on your wrist feels the electromagnetic inertial force too, and always misses the gravitational component completely. SBHarris 19:47, 21 January 2009 (UTC)[reply]

Your behaviour in the wikipedia is inexcusable, in every case, in every way.- (User) Wolfkeeper (Talk) 10:38, 21 January 2009 (UTC)[reply]

• God I want to get rid of that MEMSIC citation (ACCELEROMETER PRIMER). It’s like citing “When the wind blows, it pushes stuff around.^[5]” It looks stupid. Greg L (talk) 09:58, 21 January 2009 (UTC)[reply]

It's got the italic 'g' everywhere. You really are a piece of work.- (User) Wolfkeeper (Talk) 10:38, 21 January 2009 (UTC)[reply]

• On the (perhaps shaky) assumption that you aren’t going to claim that MEMSIC doesn’t know what they are doing, I’ve removed the {disputed} tag. If you still have stuff you want to dispute, discuss it here please. I’m not saying I’ll always be right here. But the simple stuff, is, well… simple stuff. I’ve got 15 patents on some of it has been on technical issues that were a hundred-thousand times harder to figure out that this. Discuss please. Keep an open mind. Get rid of old notions. And if I mess up, I guarantee you that just one—at most two—logical posts is all it will take to get me to admit I was wrong and turn on a damn dime. Don’t mess up articles with tags; there is no need for it. Greg L (talk) 10:09, 21 January 2009 (UTC)[reply]

Well JRSpriggs says that I am [12] correct, twice: [13].- (User) Wolfkeeper (Talk) 11:03, 21 January 2009 (UTC)[reply]

This argument is well and good. Why does it matter, at all, to this article, exactly, except that you all want so desperately to adress this argument in the article? Just excise all mention of gravity. Hipocrite (talk) 19:50, 21 January 2009 (UTC)[reply]

I hope you all don't mind me starting a new section. I've read the old ones, plus Wolfkeeper's cited book. He asked for my opinion, and here it is.

The text in question merely looks at the inertial acceleration "a" of an object in a g field. This "a" is what you're interested in, in inertial navigation, because the double time integral of "a" gives you the distance you've moved relative to the surface of the Earth, ie, the distance traveled in your 1-gee accelerated frame. This "a" is the sum of two things: one is g, the acceleration of gravity, if there is any. The other is what the book calls "f", which is the total force on the object, as you ride along with the object in it's frame (which may be accelerated, or not). This total acceleration of the object, caused by unblanced forces in the object's accelerated frame, is what gives you the total acceleration you feel in your stomach as you ride with the object, and it is what the accelerometer (mounted in the dashboard of the object) measures. It's quite correct that accelerometers cannot measure the acceleration of gravity, and neither can you feel it. All you feel is this residual total of the forces on the object in the freebody diagram, which if they are unbalanced, lead to an acceleration. None of them are gravitational: you can't feel gravitational force. What you feel is the residual of OTHER forces, if they aren't balanced. If they ARE balanced, you feel nothing--you're in an inertial frame, zero-gee, and everything floats. If they are NOT balanced, you feel that because the wall or the floor or something hits you in the feet or the rear.

Now, the text makes the matter difficult, because it simply calls all these non-gravitational forces/accelerations, "f", non-gravitational, (indeed they ARE that) and it notes that this is what accelerometers measure. Many people "know" this isn't true. If you're just sitting on the launch pad, doesn't your accelerometer register 1-gee, and you feel that? Yes, it measures one-gee, but it's NOT from the Earth's g field. What it measures is the 1-g electromagnetic acceleration of the Earth hitting against the base of the rocket, transmitted up to the floor, your shoes, and into the mechanism of the accelerometer itself. Not gravity. It's measuring an electromagnetic acceleration and EM push.

You don't believe me? Okay, if you want that same 1-gee feeling out in flat space, your rocket has to be blasting at 1-gee, and then it's clear that what your accelerometer is feeling is an electromagetic push from the nozzle on up through the rocket, and it all comes from reaction from the push off of rocket gasses. Same thing in both cases. So accelerometers on rockets blasting or hovering are not feeling gravity, and neither are they when the rocket is turned off.

Now, back to the rocket on the ground. Dig a hole under it, fire the rocket, and let it hover at 1-gee. The accelerometer still feels 1-gee and so does your gut, but now you may attribute it to gravity, same as if the rocket was sitting on the ground. But as we see, it's not. You still can't feel the gravity field. You're still feeling the EM kickoff.

Now, turn the rocket jet off, and fall into the hole which has been dug under the gantry. As you fall, you're in Einstein's elevator with the snapped cable. You don't feel the g-field. As far as you're concerned, you could be out in flat space.

Now, where does the inertial gravitational correction come in? Since accelerometers can never feel the g field, you have to know what the value of it is, and "add it" by hand to the acceleration/force the accelerometer DOES feel (which is zero), so you can tell if you're moving. Out in space, if you're blasting along at one-gee, you note that there's no g-field to subtract out, so your 1-gee is entirely "a", which means it's all inertial acceleration and you're going somewhere fast, at 1-gee inertial acceleration. But your acceleromater by itself can't tell you that, without the "hand" correction. All the accelerometer tells you is what your stomach does, and without looking through the window you can't tell if you're blasting through space at 1-gee, or hovering at one-gee on the launch pad. Do the calculation there and you have to subtract a g field of 1-gee from the 1-gee your accelerometer measures, and when you do, you find out that your "a" is zero: you're going nowhere. That's true whether your rocket is blasting to hover you over a hole, or your rocket is turned off and you're just sitting on the gantry. The accelerometer reads the same in both cases (we ignore the vibration-- maybe the simulators are shaking the thing-- how would you know?).

Finally, we look at the case where you're falling down the hole. Your accelerometer reads zero and so does your gut, but adding in the 1-gee grav field by hand, you find that your inertial "a" is 1-gee, and you're going down a hole, fast. Out in space, you don't have to add the g-field, so your accelerometer reading of zero means an inertial acceleration of zero, and you're again going nowhere.

Okay, now again note that the book says flatly that accelerometers measure a net "non gravitational" set of forces: lift, thrust, and drag. Of course the balance of thust and drag give you your horizontal acceleration, but note that the lift-force has to be large enough to balance out the gravitational force, or (if you like) the weight. The accelerometer measures the sum of them all. Now, again you can confuse yourself and consider this to be the horizontal accelerations ADDED to a 1-g downward gravitational acceleration, but that's again wrongheaded. The accelerometer again cannot see the downward gravitational component. All it measures is the airplane's resistance to it, which is electromagnetic. You have to take the downward acceleration and subtract out the gravitational field which you know to be out there, but can't measure. If you're a little light, that may mean that you're falling, or perhaps that you're flying really high and the gravitation outside is a little bit smaller than 1-gee. In either case, the inertial result (you're falling or you're in level flight) cannot be told by the accelerometer. All it measures is a total EM force, and you must know the gravitational acceleration to correct that, in order to get the inertial up/down acceleration.

Okay, I'm quitting for now. Is that clear? You should know enough to be able to change the article now so that everybody agrees. SBHarris 11:38, 21 January 2009 (UTC)[reply]

Thanks Steven, we won't be able to refer to it in terms of EM forces in the article, but what you wrote definitely is right. Everything in the world is held together with EM forces, and the paths of the forces and accelerations you've described is precisely right.- (User) Wolfkeeper (Talk) 14:07, 21 January 2009 (UTC)[reply]

There is an existing article on accelerometers. We do not have to have a redundant discussion here. Rlsheehan (talk) 14:49, 21 January 2009 (UTC)[reply]

Except that the same argument is now going on, there. Somebody has added the patently untrue fact that accelerometers measure all accelerations on them. Wrong. A falling accelerometer is OBVIOUSLY being accelerated, but it will read ZERO. Get your heads around this, and you'll be fine. SBHarris 20:10, 21 January 2009 (UTC)[reply]

• I agree with the notion that the article could likely benefit from the inclusion of a section that connects the dots between acceleration and the notion of “force.” I’ve got a draft version of something that explains the Newtonian way of looking at g-forces (which is the intuitive, natural way humans think of gravity the forces we feel as a consequence). Right now, it mentions all three of Newton’s three laws of motion. Though quite complete, it’s simply too long right now and needs a massive trim so John won’t have so much work to do. ;·) This morning, I had an idea on how to streamline it down to a tight nugget; in fact, there might not be enough room for the picture I had in mind for it. I think you’ll all be happy with it. Greg L (talk) 18:40, 21 January 2009 (UTC)[reply]

• We've been sidetracked by the idea that gravity is a "force" when in some ways it does not act like a force. A force by experience is usually something you feel, and you can't feel gravity (put you in a spaceship and you can't tell if there's a gravitational body near or not). Forces cause mechanical stresses, and gradient-free gravity (no tides) doesn't. All this is part of what led Einstein to the conclusion that gravity isn't a force at all. In our case, we merely need an intuitive reason why accelerometers don't "see" gravity. Proof: falling accelerometers, which are being accelerated, don't "know" it, and read zero. Accelerometers only read/feel "inertial forces", which are those that cause mechanical stress. That's it. But we need to lose the BAD idea that accelerometers measure all sorts and all kinds of accelerations. They don't. They only measure the one kind-- the nongravitational kind that produces mechanical stress. Example: An accelerometer sitting on the ground is not being acclerated (really, it isn't-- do you see it move? No, you don't), but it reads "1-gee, upward." An acceleration of 1 gee upward should cause it to move upward, but it's not moving upward. Why? It's reading wrong, and missing gravity. All it's reading is the force from the ground which causes the acceleration which counteracts gravity. But the gravity is not seen. SBHarris 20:28, 21 January 2009 (UTC)[reply]

• Please stop continuing your debate here. This is a page for improving an encyclopedia article on g-force in a General Purpose encyclopedia, not for debating and discussing what accelerometers do and do not measure. Hipocrite (talk) 20:31, 21 January 2009 (UTC)[reply]

• Right. And you made the same argument on the accelerometer page, when you said we should excise all mention of g-forces THERE. You can't have it both ways. Someplace, somebody needs to say what accelerometers do, and what they measure, and whether g-force is included. Where would you like? SBHarris 20:37, 21 January 2009 (UTC)[reply]

• That is a page for discussing the accelerometer article. Feel free to discuss the accelerometer article there. Do not engage in debates unrelated to the article. Hipocrite (talk) 20:44, 21 January 2009 (UTC)[reply]

• Well, you should have used that page before making changes to the accelerometer article which caused it to be in error, then, shouldn't you? I agree that THIS article is not about accelerometers, but when it mentions them and their function (*I* didn't put that in!), it should do so correctly. I've fixed it (it was almost correct, as it was). If you don't want to accurately portray accelerometers in this article at all, feel free to delete mention of them completely! But if you must have them, please discuss what they measure correctly. Thanks. SBHarris 20:55, 21 January 2009 (UTC)[reply]

The "noteable" section needs care. The example of the race car driver surviving 180 gs is amazing but questionable. The citation is not from an engineering perspective. Was the car instrumented (how?) or was this just a calculated value? Was this a "spike" in the shock pulse or was this peak observed for a while (how long)? What was the actual g-level on the driver - - not the car? This is an example of a short term shock which was not properly described and, in my opinion, not very useful. Rlsheehan (talk) 17:07, 21 January 2009 (UTC)[reply]

• You raise a very valid point, Rlsheehan. They appear to have calculated it from 108mph to zero in just over half a meter. That lessens the accuracy some and the error is frequently on the plus-side because elastic deflections in the race car’s body spring back—all the race team took into account was the permanent crunching remaining.

  I suggest we all just keep our eyes open for a better example. About a year ago, I saw a lengthy educational-channel show (I think it was the Discovery Channel ) about crash physics. They showed an Indy driver who had gone backwards into a wall and he had an accelerometer under his seat. It measured 100 g. Apparently now, many Indy car and Formula 1 cars now have accelerometers so engineers can improve crash safety.

  I don’ think I’ll be able to cite that Indy-car crash since it’s all so vague—I just clearly remember that g-force value. I suggest we all just keep our eyes peeled for an accelerometer-based crash citation in the Indy and Formula 1-car world (where all the good stuff is coming out of on this issue). And in the mean time, I see no harm in leaving the existing citation up, “108mph to zero in just over half a meter” isn’t exactly non-science; it’s a very accurate measure of the acceleration the parts of the race car nearer to the crunch zone. However, it is way, way too high a precision for stating what the driver experienced. That’s one reason I rounded it off in the chart. Greg L (talk) 18:32, 21 January 2009 (UTC)[reply]

• Here: NHTSA: [14], is a report by…

  Augustus "Chip" Chidester, National Highway Traffic Safety Administration
  John Hinch, National Highway Traffic Safety Administration
  Thomas C. Mercer, General Motors Corporation
  Keith S. Schultz, General Motors Corporation

  It says as follows: In 1992, GM installed sophisticated crash-data recorders on 70 Indy race cars. While impractical for high volume production, these recorders provided new information on human body tolerance to impact that can help improve both passenger vehicle occupant and race car driver safety. As an example, the data demonstrated that well restrained healthy, male race car drivers survive impacts involving a velocity change of more than 60 mph and producing more than 100 g's of vehicle deceleration. Such information will be helpful to biomechanics experts refining their understanding of human injury potential.

  I’ll keep on looking, but I suspect actual measured values are going to be closer to 100 g. And, like the report’s authors did (although those would be just more examples of *stupid ignorant American* practices), but also as NASA, ESA, JPL, Honeywell, Sensr, and others), it’s lowercase, roman g, (although roman uppercase G is quite common too). Greg L (talk) 19:01, 21 January 2009 (UTC)[reply]

• This report by the Vehicle Safety Research Centre Loughborough University speaks clearly to the subject of brief (millisecond) accelerations in crashes. I can tell you from personal experience, that millisecond accelerations are extraordinarily common in industry. As we had discussed before, this article needs to touch briefly on that issue to ensure our readers understand that accelerations are not just a measure of persistent gees. Oh, BTW, this study by a British University also properly uses (not surprisingly), lowercase roman g. Did I mention that in an earlier engineering job, I designed electronic equipment and had to design rubber bumpers to mitigate g-forces on the equipment in drop tests? Greg L (talk) 19:10, 21 January 2009 (UTC)[reply]

• Getting closer. Probably the History Channel. Here is the Delphi Accident Data Recorder 3 (ADR3) MS0148. It is the accelerometer mounted in Indy cars. BTW, lowercase roman g.

• Done. Revised to “>100 g” and properly cited. The old B.S. about 179.8 g has been removed from the body text. Bad science. Thank you very much, Rlsheehan, for pointing this out. You have a keen eye for stuff that doesn’t pass a proper, scientific *grin test.* Greg L (talk) 19:43, 21 January 2009 (UTC)[reply]

Whoever is screwing this article up, needs to stop. It was completely correct before. I use accelerometers in daily life. This article is completely correct--at least now that I've restored the text someone removed. Deegee375 (talk) 22:08, 21 January 2009 (UTC)[reply]

As the screwer uper, I don't dispute the information is correct. Some other correct information is that Barak Obama is the 44th president of the US. Neither the facts about accelerometers or Barak Obama belong in this article. Consider going back to my version, please. Hipocrite (talk) 22:15, 21 January 2009 (UTC)[reply]

• It’s oh-so easy to delete stuff. John and I spent hour and hours and hours collaborating on getting that text succinct, encyclopedic in tone, and correct. It speaks straight to the issue of explaining how one is at 1 g sitting in a plane and how if you pull back on the stick, the g reading goes up from there. It is an important concept in understanding the nature of accelerations. Thanks Deegee. Greg L (talk) 23:51, 21 January 2009 (UTC)[reply]

But we have textbook references that say it's not correct; and you arbitrarily deleted them, in violation of WP:NPOV and giving undue weight. You can't do that under the core values and I don't care how nice the 'encyclopedic tone' is afterwards.- (User) Wolfkeeper (Talk) 00:02, 22 January 2009 (UTC)[reply]

• No, you are simply refusing to get the point and think you WP:OWN this article. Nor can you be selective with which parts of citations you want to use. You want to use MEMSIC, which is a world-wide manufacturer of accelerometers to buttress your argument that the unit symbol is g (which is fine, because there is now some citable use), but you then can’t conveniently chose to ignore what they say in their ACCELEROMETER PRIMER. What they have is so clear, even a five-year-old can figure it out: Accelerometers are used to convert an acceleration from gravity or motion into an electrical signal. Please stop with your WP:Tendentious editing, it is simply wrong to cherry-pick the parts of citations you think serve your needs. The primer is clear as glass. Greg L (talk) 00:12, 22 January 2009 (UTC)[reply]

  The problem is that truth and clarity are conjugate variables in writing. The primer may be clear as glass, but on this point, it is wrong. An accelerometer does NOT convert acceleration from gravity into an electrical signal. An accelerometer in free fall, or in orbit, where the only acceleration on it is that produced by gravity, will produce exactly the same electrical signal as an accelerometer at rest in deepest interstellar space, where there is no acceleration on it at all, from any source. Which is to say, zero signal. Zip. Nada. It registers zero acceleration. Do you deny this? If not, then something has to give. SBHarris 01:19, 22 January 2009 (UTC)[reply]

You do have to follow NPOV, and you don't get to successfully claim that anyone that insists you follow NPOV is being disruptive. Well, you can claim it all you like on ANI; but the admins will continue to ignore you, because it's not true. And an accelerometer's job is not to convert an acceleration due to gravity to an electrical signal. That's a gravimeter; and yes you can build a gravimeter with an accelerometer, but there's other system components you need to make it read correctly. Accelerometers in and of themselves are completely insensitive to gravity, and their operation and behaviour cannot be correctly understood in ignorance of this fact. I'm therefore finding your removal of valid references that state this to be extremely disruptive and harmful to the accuracy and values of the wikipedia.- (User) Wolfkeeper (Talk) 00:34, 22 January 2009 (UTC)[reply]

• No, you are simply refusing to get the point and think you WP:OWN this article. Georgewilliamherbert was quite clear when he wrote In clear terms: There is no difference between a gravitational and an inertial acceleration, per Einstein. We're sitting in a 1-G static gravitational field. Further, a world-wide manufacturer of accelerometers says Accelerometers are used to convert an acceleration from gravity or motion into an electrical signal. You just don’t understand this technology at all well. A gravimeter is simply a high-sensitivity, high-precision accelerometer. Then there is DeeGee375 above, who uses accelerometers in daily life and he says the article is now correct. Greg L (talk) 00:47, 22 January 2009 (UTC)[reply]

You see, you still don't get it. The wikipedia works on not giving undue weight; you're cherry picking certain references and systematically remove all the other ones you don't like. And the most reliable sources say the polar opposite to your position which is solely based on poor quality sources, like manufacturers brief explanations they use to shift product.- (User) Wolfkeeper (Talk) 01:15, 22 January 2009 (UTC)[reply]

Ok, Wolfkeeper. Please explain precisely what is wrong with the following paragraph:

An accelerometer measures acceleration in one or more axis. It responds to both gravitational and inertial acceleration^[1]. If you orient a stationary, single-axis accelerometer so its measuring axis is horizontal, its output will show zero gee. Yet, if you rotate the accelerometer 90° so its axis points upwards, it will read +1 g upwards even though still stationary. If you mount the accelerometer in an automobile with its axis aligned forward with the vehicle’s direction of travel, and drive down the road at a constant speed, it will read 0 g. Yet, if you hit the brakes, it will read about −0.9 g. Accelerometers respond equally to gravity and inertial acceleration.

1^ MEMSIC: ACCELEROMETER PRIMER

Please explain clearly and exactly what it is you dispute. Then we can go to dispute resolution if necessary. Greg L (talk) 00:55, 22 January 2009 (UTC)[reply]

It's pretty clear, is it not? If you mount a one-axis accelerometer sitting on the ground, so that it is looking at the vertical axis, it reads that there is a 1-gee acceleration upwards. That is wrong. There is no acceleration upwards-- the thing is clearly sitting at rest, on the ground, d(height)^2/dt^2 =0. The definition of "acceleration" does not leave any room for compromise. Such an accelerometer as part of an inertial navigation system would tell you that you are accelerating into the sky and thus maing rapid upward distance changes. That is in error.

Now, what's wrong with this picture? I and many others have attempted to explain, and a textbook has been offered which says the same. Accelerometers do not sense gravitational force or gravitational acceleration. All they sense is non-gravitational forces and non-gravitational accelerations. In this case, the device senses the +1 g mechanical force FROM THE GROUND which is pushing it toward the sky, and reports this as +1 g, upward. It does not "see" what in the Newtonian language is -1 g of gravitational force or acceleration, balancing this to keep the device to an acceleration of zero. If you let the device fall, it does report acceleration zero, but of course that's because it's not seeing gravity then, either.

In Einstein's language, gravity isn't a force, but near Earth time and space are bent so that a force mechanical is necessary to keep something "sitting still" in curved space and slowed time, where it follows a path through 4-space which isn't the natural one, which is a geodesic (produced by free fall). But that single force is also an upward force sufficient to produce +1 g, and again the accelerometer doesn't measure anything else, because (surprise) in Einstein's view there isn't anything else. No matter how you look at it, accelerometers don't measure gravity. SBHarris 02:58, 22 January 2009 (UTC)[reply]

There's no hope for you. You're deliberately creating a non neutral article, in numerous ways, and have been doing so since you started editing here. You've also been abusive, obnoxious, insulting, you've accused me and others of being meatpuppets, you've edit warred, you've selectively removed citations, you've accused me of ignorance of basic physics, I can go on and on and on about this. I can honestly say I've only seen one other editor behave as badly as you, and he later admitted to being a paid to represent the interests of corporations. It's been real educational. Contrasts strongly with the artificially dumbed down article you're trying to create, which is actually wrong on key points.- (User) Wolfkeeper (Talk) 01:10, 22 January 2009 (UTC)[reply]

• I see. Well, I think there may be hope for you. But I think you’re busy attacking another editor rather than focusing on the single, important issue here: What the article says is the central point of any dispute. Please explain clearly and exactly what it is about the above paragraph that you dispute. You nebulously refer to something which is actually wrong on key points. Nothing can be resolved until it is clear what you think is incorrect. Perhaps then, we can learn from each other and produce wording that seems clear to us both. If not, we can go to dispute resolution if necessary. Greg L (talk) 02:01, 22 January 2009 (UTC)[reply]

Just as a naive first reader, I'd say that what is "wrong" with the paragraph is that it fails to distinguish between the facts that an accelerometer responds to gravitational force, but registers changes in inertial forces.. That is the crucial distinction. I believe that Sbharris above noted that an accelerometer in free-fall responds not to gravitational forces (other than that the accelerometer itself is accelerating, but you can't read that on the display screen - correct me if I'm wrong, but don't we enter the mysterious Mach/Einstein realm here?). The accelerometer has to be attached to something else to register a force/acceleration. An accelerometer at rest (in the local inertial frame) is a gravimeter. An accelerometer accelerating freely in a gravitational field is useless. An accelerometer undergoing non-uniform acceleration is a useful instrument. I'm on the bleeding edge of my physics knowledge, but is that helpful at all? Franamax (talk) 01:36, 22 January 2009 (UTC)[reply]

No, you've got the idea. You could be falling into a black hole, and your accelerometer would read "no acceleration" all the way down (neglecting tides). That doesn't mean it can't tell gravitational acceleration from other kinds of accelerations. It means it can't read gravitational acceleration at all. SBHarris 03:14, 22 January 2009 (UTC)[reply]

• The point, Franamax, is that an accelerometer can not distinguish between gravitational acceleration and inertial acceleration; they are all acceleration from the point of view of an accelerometer. This is what the article says, which is also what Georgewilliamherbert said above: In clear terms: There is no difference between a gravitational and an inertial acceleration, per Einstein. We're sitting in a 1-G static gravitational field. What SBHarris says about accelerometer is freefall is what the article says: they read zero in freefall. Greg L (talk) 02:01, 22 January 2009 (UTC)[reply]

• No. They are DIFFERENT from the point of view of the accelerometer. The accelerometer reads one kind, not the other. An accelerometer in free fall in a g field reads zero, even though it's clearly accelerating. Produce that same acceleration with a rocket, and the accelerometer would read it fine. So there's a difference. An accelerometer in free fall, far from any mass and in no g field, reads the same as an accelerometer in free fall in a strong g-field. Accelerometers do not see g-fields, or accelerations due to g-fields. They do see accelerations due to forces other than gravity, but not those due to gravity. I think I've said this every way it can be said. SBHarris 02:58, 22 January 2009 (UTC)[reply]

Sorry to interject, Sbharris, but you have disproved your own point - as you say, an accelerometer that is not being accelerated and far from any mass will read zero, the same reading that it will have when accelerating at one g in a one g gravity field. Hal peridol (talk) 19:30, 22 January 2009 (UTC)[reply]

Greg, sit inside the box with your horizontal accelerometer and watch the dial. If you're free-falling in space near the Earth, it will continue to register 1G or so (give or take a distant star or near planet). But this is the value you calibrated the instrument to when it was sitting on the table, so it is effectively zero, it is the reference value. If the value doesn't change, the instrument measures nothing. In a pure gravitational field, an accelerometer only measures what you set it to in the first place. It and you are just travelling along the shortest geodesic line in spacetime, which near the Earth happens to be pretty much straight downwards. Newton says that's a gravitational force that accelerates a mass, Einstein says that's the way things travel in spacetime when they're not subject to "other" forces. The floor you walk on looks flat, but it's not flat, it goes downward. Now if you get pissed off and throw the accelerometer across the falling box, it has a different inertial frame than you - and/or it is accelerating in your own inertial frame - now we can use the accelerometer and we can compare stopwatches if you threw it fast enough to approach the speed of light. These are difficult concepts... Franamax (talk) 03:45, 22 January 2009 (UTC)[reply]

• Certainly I understand all this, Franamax. The article is clearly not addressing such complexities as zeroing-out the output of a 1 g signal from (a properly calibrated) accelerometer when on earth and then going into space and reading −1 g. Any reasonable interpretation is that we’re talking about the raw, absolute output. To do otherwise is as valid as saying my AC voltage from my 120 V outlet is only 5 V (after I had zero’d it at 115 V).

  Accelerometers measure strain on internal components. Just as the article says, the only way to get a single-axis accelerometer aligned vertically with respect to the barycenter of earth to read zero is to go into a free fall. If you stand on the earth with the accelerometer aligned the same way, it will register the force of gravity just as it will if you then go into a proper-motion inertial acceleration upwards. The force of gravity when stationary on earth affects an accelerometer precisely as does accelerating at 1 g inertially from earth in space. No accelerometer, not even a light beam, can distinguish between the two accelerations; they are one in the same phenomenon. Greg L (talk) 04:00, 22 January 2009 (UTC)[reply]

• No, the force of the table or whatever is holding the acccelerometer up on the Earth, affects it precisely as does a force which accelerates it inertially at 1 g in space. Not surprising, because both are mechanical forces. The instrument is not measuring the g field, it's measuring that mechanical force. That is all these devices CAN measure. Keep the force in place (as when your accelerometer is held up a few feet in the air by a hovering rocket), and the reading doesn't change-- even if you remove the Earth. But remove the rocket and the reading goes to zero whether the Earth is there or not. So the Earth and its field has nothing to do with this reading. All it did was calibrate it, when you started by choosing your force to be large enough to make the instrument hover. SBHarris 06:23, 22 January 2009 (UTC)[reply]

Sbh, I'll take the liberty of correcting Greg to say that instead of the +1V signal changing to -1V, I'd prefer +1V changing to 0V; and where Greg compares a stationary accelerometer on Earth above, he should be rephrasing "at 1g ... from earth in space" to "at 1g in empty space" - whereupon we could all agree. We're all very close, it's just plus/minus one of something or other. The gravitational and inertial frames are exactly equivalent but subtly different. I can demonstrate this by twirling my nephew around by his ankles. Franamax (talk) 06:55, 22 January 2009 (UTC)[reply]

Wolfkeeper, I agree with your edits and philosophy in this article, but I think you should steer clear of the term "non gravitational acceleration", since I think most readers would be misled by it. For example, say I have an accelerometer sitting on the ground. I can see a reader thinking, "Well, it has no acceleration whatsoever, so it certainly doesn't have any non-gravitational acceleration!" There are plenty of clearer alternatives, like "acceleration relative to free-fall", or "acceleration, added to the quantity called 'acceleration due to gravity', which is 9.8 m/s^2 on the Earth's surface". (OK those could use improvement but I hope you see what I'm getting at.) Agreed? :-) --Steve (talk) 03:01, 22 January 2009 (UTC)[reply]

Nice point. The phrase at it stands seems... wrong, although I think I do understand the arguments made in the section above. --John (talk) 03:12, 22 January 2009 (UTC)[reply]

Please see also my post here. --John (talk) 03:14, 22 January 2009 (UTC)[reply]

This phrase (non-gravitational acceleration) has caused some problems, but perhaps it should, as it's actually accurate. The accelerometer essentially keeps track of the non-gravitational part of the acceleration (actually, the non-gravitational part of the forces) on an object. Gravitational forces can't be measured (or even felt) because they "act" on every part of a body at once, so there's no stress or strain to tell you that they're "there" or not. Which is just as well, because in Einstein's view they don't exist at all.

But we all feel the force of gravity, don't we? Actually, no. What we FEEL is the reaction forces, which are mechanical, and start at once place in our body (such as the feet) and move upward as a series of stresses. But stictly speaking, this is all non-gravitational, and that's why it all works just the same when you're in a rotating space station or a rocket, and it's the floor pushing up on you which takes the "place" of the "gravity force." Actually, these inertial forces are taking the place of the mechanical forces which are reacting to the "gravity forces," (I use quotes because of the suspect nature of "gravity forces" and the fact that they exist only for Newton). So they're all very familiar, but they're all mechanical-- caused by one atom pushing on another by chemical bonds, and so on. You never feel gravity per se at all, and neither do your instruments like spring scales and accelerometers. All you feel is these mechanical counter-reactions, which are elastic stresses and strains and compressions, etc., transmitted through the body.

. Now, a word about accelerations, which are used very loosely, but shouldn't be. If a thing isn't accelerating in our chosen frame, then it isn't, period. You can talk about its "acceleration relative to free fall," (that is, relative to an inertial frame), but that means you're talking about an accelerated frame, such as a hotel room, or a room in a rocket in space which is blasting so that everything is stuck down by inertial forces. But in both of those cases, everything in the room clearly feels only one force (the mechanical one pushing up through your feet) and you ASSUME the other one (the gravitaional force of the earth, or the inertial force of the accelerated frame in a rocket, caused by the rocket motor) only because you know that forces need to be balanced when things aren't in motion, and in your frame, things are not moving. Thus, everything you see which is not moving in your frame, you presume to have (in Newton's view) two forces on it which balance each other; but only one of which you can measure, and the other of which you assume to exist, only because things have no motion (in your frame-- again, we're taking about things like a glass of water or an accelerometer on a table, in a hotel room on earth, or in a room in a rocket). So a thing on a runway has no acceleration (net, gravitational or otherwise), but we presume that it has two balanced types of forces: one gravitational and one mechanical (acting up from the ground). It's useful to view these Newtonianly as two balanced forces, but it's not useful (I find) to view them as two balanced "accelerations." But you can, if you like.

Now, accelerometers, like spring scales, don't really measure accelerations directly, but rather measure forces. Accelerations are assumed from knowing the mass of the parts. And the forces we can measure (with both the spring scale and the accelerometer) are mechanical ones, NOT gravitational ones. They are caused by the electromagnetic force of the fundamental forces, not by gravity. The gravity force isn't felt, and not measured.

That's why we're at pains to say that accelerometers only measure NON-gravitational forces (and non gravitatinal accelerations). When you think you're using them to measure gravity, all you're REALLY doing is measuring the mechanical counter-reaction, and assuming that gravitational forces/accelerations are the same, in very special situations where you know they must be.

Of course, the general fact may or may not be true, and usually isn't. Usually, what the gravitational field is in the vertical direction is, is an unknown, and must be "input" from an outside source, like a lookup table. For an accelerometer sitting quietly and motionlessly on a bench or in an instrument panel on a run-way on Earth, it's a good bet that the mechanical counterforce it's measuring (caused by the pressure of the mountings, transmitted through the body of the device to some sensitive element like a crystal inside), is the SAME as the gravitational force/acceleration acting on the thing. It has to be, because they must balance out if the thing isn't moving up and down, and we can SEE that it isn't (this becomes a problem when we don't know if it is or isn't, as in an airplane in clouds at night). In such cases, it's said that the accelerometer is measuring the acceleration of gravity, but all it's doing is measuring the acceleration of the counterforce, and the equality of the gravitational "force" or acceleration, is assumed. In fact, you really can't usually assume such things. Inside a blasting rocket, for example, there is no gravity and the "counterforce" (the force from the instrument mounting) is all there is. Sitting on a bench or runway, the device says "+1 g acceleration, upward." In the Newtonian view, you see it's not going upward, so you assume that the +1g force/acceleration it's measuring is being counteracted by a -1 g gravity field, acting downward. But the device is not measuring gravity or gravity force, it's measuring the electromagnetic counter-force.

The reality of this is apparent when you get away from places where you know what your position and "actual acceleration" (relative to some reference) really are. In such situations, you find that the accelerometer really only measures the non-gravitational component, and NO gravitional one. For example, if you're in a spaceship falling into a black hole at 10 g's, and also blasting sideways (or any direction) at 0.2 g, all your accelerometer will read is "0.2 g." It's not measuring the field you're falling into, but only measuring the inertial force/acceleration created by your rocket engine. You, in your rocket seat, may feel a sort of inertial force that feels like gravity and pulls you toward the floor, but your faithful accelerometer doesn't see it that way. It's bolted to an instrument board and held fixed relative to the rocket engine, and so all pushes by the rocket engine are transmitted to it directly, where they are read simply as non-gravitational forces/accelerations, period. Very simple.

In an airplane the same thing happens. The accelerometer only measures the sum of all the mechanical (non gravity) forces/accelerations on it. For sideways motions these are straightforward, but for up-and-down, you no longer have the luxury of presuming the device measures gravitational acceleration indirectly. All it measures is the total up and down reaction forces/accelerations, and you must tell it by hand what fraction of these are due to the Earth's g-field, so that it can presume the rest are caused by mechanical positive and negative lift forces (which are analogous to the pressure of the runway against the wheels of the plane, but now can be less or more than the plane's weight, and less or more than local g). It is only these last which contribute to vertical position (change in altitude) when integrated. At every altitude and time you must "tell" the device how heavy it should be if it weren't moving up and down, and then it must measure how heavy it actually is (mechanical acceleration) and take the difference to get vertical inertial acceleration which must be paid attention to, as it's a marker for changes in vertical velocity and position. Again, the accelerometer is not summing gravitational acceleration and vertical mechanical acceleration. Rather, it feels only the latter, and totally neglects the former. SBHarris 08:43, 22 January 2009 (UTC)[reply]

This phrase (non-gravitational acceleration) has caused some problems, but perhaps it should, as it's actually accurate.

No, it shouldn't. While accurate, more than 99% of readers would misunderstand it. Please read the point 5 of WP:NOT PAPERS. -- Army1987 – Deeds, not words. 12:29, 22 January 2009 (UTC)[reply]

I'm with Army1987. Sbharris, if you read what I wrote originally , you'll see that I was not arguing that the phrase "non-gravitational acceleration" is incorrect. Quite the contrary, I already 100% agree that it's correct, and I'm sorry that you spent so much time typing the above text to defend its correctness. My point was that the phrase is liable to be misinterpreted by the average reader, and therefore should be avoided. There are plenty of other words in the English language, we can find another way to say it that is equally accurate but that every reader will understand. --Steve (talk) 17:12, 22 January 2009 (UTC)[reply]

Well, how about saying an accelerometer measures the component of acceleration which causes mechanical stress? That's what you feel with your butt against a chair, as in seat of the pants flying. And the reason for this, is that inside every accelerometer, there's a thing which corresponds to your butt, and another that corresponds to the chair, and something that measures the interaction (pressure/stress) between them. So an accelerometer, in a way, is just a mechanical ass with an electrical output. It doesn't measure gravity directly anymore than your butt does. SBHarris 22:40, 22 January 2009 (UTC)[reply]

I was stopping here to say "kudos" for this article. It is a very clear explanation of how accelerometers work that I could not find elsewhere. I really liked the part where acceleration is explained as km/hr per second. That makes it SO MUCH CLEARER for my students. Good work. Wikipedia is quite a resource. —Preceding unsigned comment added by 66.108.31.53 (talk) 03:14, 22 January 2009 (UTC)[reply]

Are you being sarcastic? Somebody has stripped the article of all references to accelerometers in any case. SBHarris 03:21, 22 January 2009 (UTC)[reply]

The term "gravitational acceleration" can mean 2 things. It can mean the acceleration (relative to an inertial reference frame) that a physical object actually undergoes in response to gravity, for example when it's in free-fall. Obviously this quantity isn't measured by an accelerometer, since accelerometers read "0" in free-fall. "Gravitational acceleration" can also mean the quantity g, 9.8 m/s^2 at the earth's surface. Obviously this quantity can be measured by an accelerometer, for example by placing it on the ground and reading the dial.

No. The reading on the accelerometer on this case is merely a reading of the force the table (or whatever it's sitting on) is exerting on the accelerometer. It's mistaken for g because it's the same number as g, if the thing happens to be sitting still--- but the device is not actually measuring g. Demo: replace the legs of the table with 4 rockets that keep the table hovering at constant height. The reading on the dial doesn't change. Now (the magician trick), remove the Earth and its gravity field. The reading still doesn't change. Why? Because it never had anything to do with the gravity field. It just happened to be the same number, because you (perhaps inadvertantly) calibrated it by fixing up your support system's force, so the accelerometer didn't move up or down, when the Earth was there. But the force of the support system is what is (always) being measured. Further demo of this: remove the support, and the dial goes to zero, whether the Earth is there or not. SBHarris 06:06, 22 January 2009 (UTC)[reply]

I measure my height by marking the top of my head with a pencil on the wall, then measuring with a tape-measure how high the pencil mark is. Does that mean the tape measure isn't actually measuring my height? Well, yes and no, but more to the point, who cares? The real point is that with a bit of effort we can think of creative alternatives that are completely unambiguous, and the first step is to collectively abandon phrases like "measures / does not measure gravitational acceleration" that a reader can interpret in more than one way. I mean, if we're able to spend hours debating how to interpret this particular phrase, a non-physicist reader in a hurry has no hope at all. :-) --Steve (talk) 08:04, 22 January 2009 (UTC)[reply]

As far as I can tell, Wolfkeeper has using the first definition and others have been using the second one, and y'all have been arguing past each other on and on. So instead, maybe we can agree to not use the term "gravitational acceleration" in the article (at least not without additional clarification) and put your time instead towards finding a different, creative and concise and unambiguous phrasing. Maybe a starting point could be:

"g-force is a measure of an object's acceleration relative to free-fall. For example, an object sitting on the ground is stationary, but is accelerating at 1g relative to how it would be moving in free fall, so its g-force is 1. If it's accelerating upwards at 1g relative to the earth, it's accelerating upwards at 2g relative to free-fall, so its g-force is 2. In space, there is no free-fall acceleration, so the g-force measures acceleration directly. More generally, g-force is the vector sum of [blah]".

A more concise one, maybe for the intro: "g-force measures the total effective force that one feels due to the combined effects of gravity and acceleration". --Steve (talk) 03:25, 22 January 2009 (UTC)[reply]

• Thanks Steve. That helps. Greg L (talk) 03:45, 22 January 2009 (UTC)[reply]
• That's likely more clear than my attempts above, however for the "average" reader, I'd prefer to see something more accessible in the intro. Something along the lines of "remember when your Dad used to swing you around?" or "remember when you first had a car and took that corner in the gravel and got thrown across the entire front seat?". Not quite that corny, but is there a way to convey a human experience first, before delving into the theoretical and technical details? Franamax (talk) 04:00, 22 January 2009 (UTC)[reply]

• I would have thought that what is currently in Nature of the measure, which talks about stopping and turning in a car, ought to be pretty familiar to anyone in the English-speaking world—even a very young child. Moreover, that section now makes the measure more accessible by expressing it in terms that are far, far easier to comprehend than “9.80665 m/s²”, it introduces the measure by telling how that complex-looking thing can be expressed as 35 km/hr per second or 22 mph per second. I can’t imagine how the subject of acceleration be made any simpler than that. Greg L (talk) 05:16, 22 January 2009 (UTC)[reply]

Well yes, but at the same time that is a profoundly exclusionary statement, since it cuts out all of those who don't ride in cars, and the greater subset who don't see a speedometer on a regular basis. Point taken however. Franamax (talk) 07:13, 22 January 2009 (UTC)[reply]

Greg, I'm on a global interpretation bent right now, wrestling with Canada Census Ethnic Origin data, accuracy, presentation and interpretation - so please bear with me when I insist there should be something for the truly average global reader. :) Franamax (talk) 07:13, 22 January 2009 (UTC)[reply]

The article currently reads: "The measurement of g-force (or g-load) is the measure of an object's acceleration—gravitational and inertial."

Now me reading that would naturally assume that you add the inertial acceleration to the gravitational acceleration. I would also assume that there's only one way to measure an object's acceleration. I mean otherwise it would have said that, right? In English, you try to communicate by saying things that the other person probably doesn't know about. "I saw Fred the other day with that woman". But you wouldn't say that in anything but a sarcastic sense if the woman you saw him with was his happily married wife.

Here, adding the two accelerations is exactly what you don't do: you SUBTRACT the gravitational acceleration from the inertial. Now the argument has been made more or less, that we shouldn't try to 'confuse' readers by bothering them with 'unnecessary' details like that, but all I see is an entire article that probably overall explains the topic in such a way that it cannot be correctly understood. I think we need to credit the readers with some intelligence, give the accurate definition at least somewhere, and give a few good examples (and there's already some in the article).- (User) Wolfkeeper (Talk) 14:34, 22 January 2009 (UTC)[reply]

OK, how about "g-force measures the total effective 'force' that one feels due to the combined effects of gravity and acceleration. The g-force is defined to be "1 g" for a stationary object subject to gravity on the earth's surface, and would be "0 g" in any 'weightless' environment such as free-fall or an orbiting satellite, and can be greater than "1 g" in a rapidly-accelerating rocket, for example. More precisely, if a is an object's acceleration vector, and g is the gravitational acceleration vector (pointing towards the center of the earth), then the g-force for that object is |a-g|/(9.8 m/s^2) g's." --Steve (talk) 17:26, 22 January 2009 (UTC)[reply]

• F = ma applies to any object accelerated relative to a given frame of reference—usually you. If you want to stand on the earth and watch something drop, then force F in this case is gravity (without the opposing equal force of the ground pushing up) and the object accelerates relative to you. If you are falling with the object, it is stationary with respect to you and the only way to get the object to accelerate relative to that frame of reference is to apply some other force to accelerate the object.

  These are nuances that are well beyond the scope of this article. Readers can click on the links to Newton’s laws of motion to learn more. This article makes it clear that gravity is a 1 g force and inertial accelerations with respect to the earth add or subtract to this ever-present force. Even still, this article speaks to the issue of free-falling bodies (like amusement park rides) to ensure readers have all the important basics down. Greg L (talk) 22:08, 22 January 2009 (UTC)[reply]

• The "G-force" is ordinarily used only to quantify what a person "feels" (or would feel if there was a person there). Thus, a person falling into a black hole at 1000g's feels no G-force. Ironically, what an accelerometer measures is not total acceleration, but only that part of acceleration which a human would feel, and the part that causes g-stress, or g-load, or otherwise breaks stuff. Accelerometer output is a perfect proxy for what a human riding with the accelerometer would feel; it gives a quantitative output of that. So acclerometers don't measure acceleration, they measure stress due to acceleration. They measure the acceleration which can be felt. This is not surprising, because the instrument isn't magic, and it can't measure (given a suitably large efffect) anything a human cannot feel. The seat of your pants is a crude accelerometer, and the accelerometer only gives you quantitatively what your butt tells you qualitatively. SBHarris 22:29, 22 January 2009 (UTC)[reply]

I hate to open another debate on this page, but there's some material in the article that's misleading.

If I place a book on a table, the force of gravity on a book and the normal force that the table exerts on the book are not an action-reaction pair. (I mentioned this in passing above, but didn't realize it was in the article as well.) They are equal and opposite force, but both act on the same object, and have a different fundamental nature (gravitational and electromagnetic respectively.)

Newton's third law is all about interactions; that when object A acts on object B, object B acts on A as well. It's stating that every force is really part of a mutual interaction between two objects. In the example above, as the earth acts on the book, there is also a gravitational force acting on the earth. And as the table exerts a normal force on the book, the book exerts a normal force on the table.

I know this sounds a little pedantic, but as a TA I have enough trouble explaining this to students after they miss this on a test, without Wikipedia misleading them... :) --Starwed (talk) 08:28, 22 January 2009 (UTC)[reply]

Yes, the weight of the book is an action which acts on the table and it is in the reaction pair with the normal force of the table that acts on the book.- (User) Wolfkeeper (Talk) 09:36, 22 January 2009 (UTC)[reply]

• Welcome to Wikipedia. Yes, there is a lot of material in this article which is misleading and just plain wrong. The idea that accelerometers “measure” gravitational acceleration, for example, is wrong. You’ll see some nonsense that the reading of an accelerometer in an airplane sitting on a runway indicating +1 g (upward) is due to the Earths’ gravity somehow accelerating the sitting airplane “upward in spacetime” (as though spacetime had a direction we could call “up”), and the accelerometer is supposed to know this and somehow measure it (actually, the accelerometer merely measures a force on a load crystal which it interprets as an upward inertial acceleration, which it would be, in absence of a gravity field, and outputs that because it doesn’t “notice” gravity). All this would be funny, but one editor is insisting on this kind of stuff and I suspect he’ll eventually simply have to be suppressed by force. Like I said, welcome to Wikipedia.

  As for the rest, it would help if you’d point out exactly the parts you’re having trouble with, or better yet, just go in there and change them, so they read right to you. I’m eventually going to have to do that myself, as soon as I get done with this TALK page discussion about all this (go there and have a look).

  For certain, Newton’s third law applies only to single force of a given type, so you have to have two separate vectors, each with two ends/heads. The attractive one is for the gravitational force on a book (let’s pretend that exists, ala Newton) and repelling one is for the “electromagnetic” normal force, too (the one that supports the book against the table it sits on). I like to write attractive force vectors like this <--- ---> and repelling ones like this --- > < ---

  They both exist, side by side for the book, the attractive one for gravity and the repelling one for the normal force. Let’s turn gravity on its side for a moment because the vectors are easier to draw: we’ll put the table and the Earth on the left, and book on the right. The vector arrows for each force are equal for the 3rd law, and there are two of them, one for each force. The same length gives us the 3rd law constraint that the normal force vector pushes as much on one end (the book) as it does on the other (the table), and also the same is true for the gravity vector that pulls two things together.

<--- --->

TABLE --- > < --- BOOK

What confuses students is what you then do, after getting done with the third law, is isolate the book as a free-body, and then it’s permissible to draw “half-vector” forces to it. There’s a gravitational force that pulls the book toward the table. There’s another equal force (not action/reaction pair, but equal or else the book would be in motion) which is the normal force pushing the book upward:

Normal force --- > BOOK <-- Gravity

These forces sum to zero so the book doesn’t move, and that’s Newton’s second law.

In the relativistic view, things are more complicated and only the normal force exists. It causes an acceleration off the 4-D geodesic path, where ordinarily the object would fall and thus undergo time dilation, and have its proper time (the time that passes for it) maximized for the world-line it follows. Instead, by being accelerated by the normal force, it takes another path. But the point is that the unbalanced force still causes a sort of acceleration from the geodesic in 4-D, even though it’s difficult to draw in 3-D.SBHarris 10:19, 22 January 2009 (UTC)[reply]

Wolfkeeper, put a bowl containing some water on a scale. Then, take a stick and partially immerse it into water, holding the other end still in your hand above the water's surface. Do you expect the reading of the scale to change, and why? Now, perform the experiment; if the result is not what you expected, try to figure out why. If you think you've got it, try to predict what would happen if you used another stick with similar size but very different density. Then, actually perform the experiment. Was the result the one you expected? (Hint: Starwed is completely right.) -- Army1987 – Deeds, not words. 12:36, 22 January 2009 (UTC)[reply]

Buoyancy and Newton's third law; I don't even need to do the experiment. ktxbai. (p.s. not net buoyancy, so it's independent of density) Yes, he's completely right, never said otherwise.- (User) Wolfkeeper (Talk) 12:53, 22 January 2009 (UTC)[reply]

I had misunderstood your post, then. Now that I've read it more carefully I understand what you meant. -- Army1987 – Deeds, not words. 14:14, 22 January 2009 (UTC)[reply]

I agree that the article lead kinda, sorta, almost defines what g-force is, in a way, however WP:NOTDICDEF states:

articles should begin with a good definition and description of one topic

WP:GOODDEF states:

"A definition aims to describe or delimit the meaning of some term (a word or a phrase) by giving a statement of essential properties or distinguishing characteristics of the concept, entity, or kind of entity, denoted by that term." (Definition)

A good definition is not circular, a one-word synonym or a near synonym, over broad or over narrow, ambiguous, figurative, or obscure. See also Fallacies of definition.

In other words, by (as it turns out very old, good) policy you are not allowed to be very vague on what this is just to make it read well or if you are concerned about 'confusing people'. The way to not confuse people is just to explain it really well. This is also what the WP:LEAD guideline says.- (User) Wolfkeeper (Talk) 09:32, 22 January 2009 (UTC)[reply]

Only time for a quick comment, having come here from WP:AN3.

1. Stop edit warring or you'll get blocked :-) But I think this has mostly happened. Good.
2. Looking at [15], both sides appear wrong. As has been said above, gravity is acceleration and accelerometers measure acceleration. IMHO mentionning gravity at all in the lead just confuses. Just say "The measurement of g-force (or g-load) is the measure of an object's acceleration" and stop there.

William M. Connolley (talk) 14:42, 22 January 2009 (UTC)[reply]

I've closed the AN3 thread with a result of "peace". This had better be true William M. Connolley (talk) 19:01, 22 January 2009 (UTC)[reply]

Some edit warring is inevitable is one party has some wrong idea about something as clear as the function of a basic instrument of physics, and keeps pushing it. Wikipedia really doeesn't have any good answers for what to do, then, as no consensus will ever be reached.

The article on G-force (this one) might be improved (or the fighting stopped) if all mention of accelerometers was removed, but the fight is inevitable on the Accelerometer wiki.

Accelerometers ONLY measure only some kinds of acceleration. They do not "see" the acceleration produced by gravity. Thus, an accelerometer dropped in a g-field, which is surely accelerating, will read "zero," just the same as if it was out in space, floating. In the same way, an accelerometer held hovering over the Earth with a rocket, will read +1g, but that figure will not change if the Earth is then removed, along with its gravitational field. ERGO, the accelerometer never saw that field, or noticed the presense of the Earth, either.

Ironically, what accelerometers DO measure, is the total non-gravitational acceleration on an object, and THAT is what a person feels, and THAT is what is measured in units of "g-force." So that's really the reason probably why the instrument creeps back into this acticle, although nobody has clearly articulated that, yet. For example, an astronaut in orbit is still well within the Earth's g-field, but feels no g-force (absent micro-tides) and his accelerometer agrees with him, and also reads "zero-g". So this instrument is a convenient way to measure the thing that we'd like to quantify in this article. The problem is that this article is all screwed up, and nobody has yet defined it very well. The "G-force" is the mechanical thing-- it is the sum total of all mechanical forces on a body, and does not include gravitation (really, it doesn't). If it's zero, you float; it doesn't matter what gravitational field you're in. If the g-force on you is high (for whatever reason, whether or not your being squashed by Jupiter or squashed by being shot from a cannon) then the g-force on you is high, and your accelerometer in your pocket will tell you exactly how high. It's the perfect readout for your g-force stress. "But wait," you said, "you mentioned Jupiter." So I did. But if you're falling into Jupiter, you have no stress (and your accelerometer reads zero and you feel weightless). BUT if you're held above Jupiter in a balloon, the stress on you is not from Jupiter, it's from the platform of the balloon which is trying to keep you from falling. The G-force you feel is from the floor of the balloon cabin, and that's the force your accelerometer feels as well. And will read out as an "acceleration." But it's only the "accleration a human would feel." It's not the sum total of every acceleration you can think of. SBHarris 22:03, 22 January 2009 (UTC)[reply]

No, that's completely incorrect - see Equivalence principle. Being in a gravitational field of 1 g cannot be distinguished from accelerating at a constant 1 g by an observer (including an accelerometer). Note that in your example above, an accelerometer being held stationary above the Earth in a rocket is still not accelerating. Hal peridol (talk) 23:25, 22 January 2009 (UTC)[reply]

Help me out. I don't see a single thing you've said which contradicts anything I said. Great name, BTW. Are you some physicist we know, who's gone off their Haloperidol? If you're a sock, beware. SBHarris 23:46, 22 January 2009 (UTC)[reply]

Wolfkeeper. The below paragraph serves as a template for the remainder of the Gravitational and inertial acceleration section. That section builds upon that paragraph. Let’s start there. Please explain precisely what is wrong with the following paragraph:

An accelerometer measures acceleration in one or more axis. It responds to both gravity and inertial acceleration^[1]. If you orient a stationary, single-axis accelerometer so its measuring axis is horizontal, its output will show zero gee. Yet, if you rotate the accelerometer 90° so its axis points upwards, it will read +1 g upwards even though still stationary. If you mount the accelerometer in an automobile with its axis aligned forward with the vehicle’s direction of travel, and drive down the road at a constant speed, it will read 0 g. Yet, if you hit the brakes, it will read about −0.9 g. Accelerometers respond equally to gravity and inertial acceleration.

1^ MEMSIC: ACCELEROMETER PRIMER

Please explain clearly and exactly what it is you dispute. Then we can go to Wikipedia:Dispute resolution if necessary. Greg L (talk) 18:32, 22 January 2009 (UTC)[reply]

Even in the bizarre world you inhabit, it should be self-evident to you that accelerometers don't respond equally to gravity in the same way as other accelerations. If I accelerate an accelerometer downwards it registers positive g downwards. If I have an acceleration due to gravity- gravity is always downwards, but the accelerometer shows positive g upwards. It therefore isn't even in your terms 'equal' anymore than -1 = 1 - they respond oppositely to gravity than other accelerations.- (User) Wolfkeeper (Talk) 20:28, 22 January 2009 (UTC)[reply]

And if I let it fall- it accelerates- downwards (at, by shear coincidence 9.81m/s^2)- giving a reading downwards, and it adds that to the acceleration due to gravity (which is unchanged)- and reading upwards; and gives a total zero reading. Right? They're not equal. One is inverted to the other. Equal and opposite.- (User) Wolfkeeper (Talk) 20:28, 22 January 2009 (UTC)[reply]

• When you begin a post with Even in the bizarre world you inhabit, you are being confrontational, are being uncivil, and make it exceedingly difficult for other editors to take you seriously. I suggest you go cool off and come back when you can be constructive and engage here in good faith. Fortunately, I’ve got a pretty thick skin and have little inclination to go run off to mommy and complain about how some such editor is calling me “a poopy head”. But if you want to enjoy the privilege of posting a {disputed} tag at the top of the article, it’s time you started getting into the saddle here and abide by the rules of Wikipedia.

  More importantly, I’ve repeatedly asked you to explain precisely what it is about the text that is in error and we are repeatedly met with explanations about how you think the world works that only leaves us guessing as to what you think is wrong with the text. So…

  Please copy the above passage, paste it below, strike what you think is inaccurate, follow it up with what you think is the correct language, explain your reasoning, and cite your basis.

  Now, so we don’t waste time on fundamentals, no accelerometer in the world can tell the difference between sitting on your desk, where it is being exposed at 1 g to the force of gravity, and sitting inside a space ship which is accelerating out in space away from earth at 1 g. To the accelerometer, they are absolutely identical and indistinguishable. Even to a light beam the two accelerations are absolutely identical. Further, if you turn a single-axis accelerometer 90° on your desk, it will read zero. And doing the same thing to the accelerometer in the space ship would have the exact same effect.

  I suggest that if what you are driving at is some sort of nuance that goes beyond this, it may well be beyond the scope of this article. Greg L (talk) 20:51, 22 January 2009 (UTC)[reply]

• What you're missing is that the accelerometer on your desk is not reading 1g because of gravity. It is reading 1g because the desk is pushing upward on it. Gravity is merely the reason why this push doesn't cause it to MOVE upward, but the accelerometer only measures the mechanical push, and the mechanical stress, and doesn't care whether this causes motion or not (and has no way of telling, all by itself). In every situation, the acclerometer in your pocket only measures the accelerational stress on your body. This is completely independent of what gravitational fields might be around-- they could be large or small or nonexistent, and it doesn't matter to the accelerometer. It doesn't see any of them. SBHarris 22:15, 22 January 2009 (UTC)[reply]

• If a large gravitational force were to suddenly appear next to someone with an accelerometer, for example a new supermassive black hole, then that would definitely register on the device. The claim that it (the device) would not see any of them (gravity fields) is incorrect.WorkingBeaver (talk) 22:56, 22 January 2009 (UTC)[reply]

• The equations of relativity don't allow for masses to "appear" or "disappear", as this would violate conservation of energy-momentum, etc. Consequently we don't know what would happen if a mass appeared out of nowhere; there aren't even any equations for it. However, if a black hole (or any other mass) were to "sneak up on you" in the conventional way, you definitely would never feel it (save for the tides).

• You wrote above "that figure will not change if the Earth is then removed, along with its gravitational field". You just described the Earth suddenly being removed, i.e. disappearing. You just contradicted yourself. A super massive black hole moving towards someone would definitely be felt by the device.WorkingBeaver (talk) 23:40, 22 January 2009 (UTC)[reply]

• You’ve come a long way, Sbharris, in understanding this. You first started off by stating that gravity is a mechanical pressure from an electromagnetic force [16] No, I’m not missing anything. What you are missing is that the accelerometer is reading 1 g because of two forces: gravity pushing down on the entire accelerometer (including its contents), and the desk pushing up on the accelerometer’s body.

  I’m thinking I should add that wording to the article. Greg L (talk) 22:29, 22 January 2009 (UTC)[reply]

• Stop misquoting me! I never said gravity was due to pressure from an electromagnetic force. I said what you THINK you're feeling as "gravity" is pressure from an electromagnetic force. Your gut, the seat of your pants, and your accelerometer only measure acclerations that produce mechanical stress, and the stress is what they measure. An object falling in a g field has both grav acceleration, AND inertial acceleration. But there is no stress on it, and thus an accelerometer carried along will read ZERO. It does not measure sums of accelerations, it (effectively) only measures differences between them. And those differences can be zero, even though the accelerations are still there. SBHarris 23:25, 22 January 2009 (UTC)[reply]

Here's the table of accelerations:

You tell me Greg_L self-styled physics guru, self-styled expert article writer, why is the sense opposite in the above table?- (User) Wolfkeeper (Talk) 22:24, 22 January 2009 (UTC)[reply]

• Please answer my question. No one here can read your mind. Greg L (talk) 22:29, 22 January 2009 (UTC)[reply]

The first two sentences are half-truths that are basically wrong. The last sentence is completely wrong, as the table shows. The rest of it is OK, and on the upside is enough for a really alert or careful reader to realise you're talking complete garbage overall, and would alert them to the need to go somewhere where somebody actually took the time and effort to get it right.- (User) Wolfkeeper (Talk) 22:48, 22 January 2009 (UTC)[reply]

• As I wrote above, please copy the above passage, paste it below, strike what you think is inaccurate, follow it up with what you think is the correct language, explain your reasoning, and cite your basis. Greg L (talk) 23:02, 22 January 2009 (UTC)[reply]

We’ve now got an article on g-force that explains acceleration in more familiar, accessible terms than one often finds at NASA and other scientific sources. It now finally explains a very important aspect of g-force: the role of *force* in accelerations. Next, it is probably time for a short intro to Jerk (physics). That article includes this sort of stuff:

…which isn’t highly accessible to a wide audience. I would propose to add a short section on jerk. This article, g-force, is where many readers would first go to try to learn of such a thing since hardly anyone would know to type “jerk” or “Jerk (physics)” into our search field. Here, we can briefly introduce the concept, explain it in terms that make it extremely easy to conceptualize (I have a couple of ideas), and then link to the main article. Greg L (talk) 19:47, 22 January 2009 (UTC)[reply]

I would prefer that type of discussion be in the Shock (mechanics) article. Jerk only applies to transient shocks and not sustained g-forces. The shock article could use a little input on jerk and on dynamic response to short term shock. Rlsheehan (talk) 22:11, 22 January 2009 (UTC)[reply]

• Along with touching upon the subject of sinusoidal accelerations (shaker tables, for instance) to ensure readers don’t walk away from here with the notion that g-force is only a long-term phenomenon, John had also suggested we touch upon jerk [17]. I agree with him on both counts; briefly touching upon jerk here and linking to the main article would serve a valuable end. Greg L (talk) 22:19, 22 January 2009 (UTC)[reply]

SBHarris and Wolfkeeper I am going to have to ask that both of you stop editing the article and only continue to talk on this page and that you both calm down. This is because it has become apparent from reading your contributions that you do not fully understand the subject and that your increasingly heated edits are damaging the accuracy of the article, so I think it is better that both of you try to talk here to understand the subject better before trying to contribute to the article page. WorkingBeaver (talk) 23:49, 22 January 2009 (UTC)[reply]