Talk:Pressure

Numbers in table are not consistent

The numbers in the table of conversion of units are not consistently written: numbers are separated with commas, periods and spaces. For example it says 1 psi = 6,894.76 Pa and 1 at = 98 066.5

P or p

In physics there are some conventions (that are broken all the time). Isn't it standard to denote pressure (or power) as P and momentum (or a proton) as p? A standard should be set. Alejandr013 21:08, 14 August 2006 (UTC)

I've seen some physics textbooks that use p for pressure, and some that use P. I don't think there's any widely followed convention.--75.83.140.254 01:59, 10 December 2006 (UTC)

Pressure definition

I would say that pressure is the application of force upon a static body. Once the body moves, it is being pushed. In gravity-free and atmosphere-free space, no further pushing is required for the body to keep its inertial motion.

Good point, but that's more of a dicdef than an encyclopaedia entry. Noel (talk) 12:17, 6 Dec 2004 (UTC)

Actually, that's an inaccurate definition. Pressure is defined as the magnitude of the normal force per unit area, regardless of whether the boundary upon which it acts is static or dynamic. --Simian, 2005-09-27, 19:13 Z

To send an electric signal through a push-button, as in an elevator, the button is pushed all the way until it causes some pressure for the electric contact, unless it has been designed to act as a switch. --Ghitis 15:49, 12 Aug 2004

I removed the words "component of the" from the pressure definition so the definition would be correct and would match credible physics books. Using the incorrect terminology "normal component of the force" means there's a nonnormal resultant force, which isn't the case in many pressure problems. There's no shearing force in nonviscous fluids nor static viscous fluids. In contrast, the wording "normal force" covers all cases and is the correct definition used in credible physics books. "Pressure is defined as the magnitude of the normal force per unit area." --Simian, 2005-09-27, 19:13 Z

Pressure is not defined just for nonviscous fluids. It doesn't have to be the case in "many" examples of pressure (though it in fact is); one case would be sufficient. There is no reason why any "component" of the force cannot be zero, and there is no reason any component cannot be all of it. The tangential component could easily be nonzero in that thumbtack example, couldn't it? Gene Nygaard 04:08, 28 September 2005 (UTC)

Yes, since the thumbtack is a solid, it can resist shearing stresses. Nonetheless, the presence or absence of shearing force (for solids or viscous fluids) doesn't alter the definition of pressure. The definition in physics books applies equally to all cases (solids and fluids). --Simian, 2005-09-28, 05:05 Z

Sure. That's what "normal force" means; the component of the force which is normal to the surface on which the pressure is being measured.

But people who don't know that are going to have a damn hard time figuring it out from the links given here. Gene Nygaard 12:59, 28 September 2005 (UTC)

A normal force is a force perpendicular to a surface, which is explained at the link. A component means part, not the whole. In vector mechanics, component means two or more vectors whose vector sum equals a resultant vector. A so-called "component" equal to zero is nothing, and is therefore not referred to as part of a resultant force. And a force isn't called a component if it's not less than a resultant force. If a normal force is the only force applied, it isn't called a component of another force. Nonviscous fluids and static viscous fluids have no shearing forces, so the wording "normal component of the force" doesn't make sense for static fluids (because the only force is the normal force). The words "component of the" would apply only for solids and viscous fluids, but then only if shearing forces are present, thus making the definition nongeneral. In contrast, the wording "normal force" covers all cases (solids, viscous fluids, and nonviscous fluids) and is the correct definition used in credible physics books. "Pressure is defined as the magnitude of the normal force per unit area." --Simian, 2005-09-28, 23:09 Z

Good grief. Pay attention to the world around you.

http://www.ee.oulu.fi/~kapu/SCIApap.pdf In Fig. 1, the behaviour of the y-component is shown when the x-component equals zero. The horizontal axis represents the y-component, whereas the vertical axis represents the z-component. Now if a normal vector is rotated ..."

http://www.ae.gatech.edu/people/dhodges/courses/Rigid-BodyGAF.pdf "Note that the a1 component is a bit messy, but since the horizontal component of force is zero"

http://www.feec.vutbr.cz/EEICT/EEICT/2003/msbornik/04-Power_Electrical_Engineering/02-Mgr/03-xvalen03.pdf "The z component of force is zero"

http://www.public.iastate.edu/~jpete24/EM324/Lecture%2025.pdf "the Axial component of force is zero"

That is, of course, often the goal in ratation of coordinate systems; to get components that are equal to zero. That terminology is used all the time. Gene Nygaard 01:28, 29 September 2005 (UTC)

Yes, the projection of a force onto a perpendicular axis is no force. Even though this is referred to as a component, it's not a force. Nonetheless, to say that a resultant force itself is a component of the resultant force itself, being only more confusing, wouldn't improve the article or definition at hand. That's why the wording "component of the" isn't included in the general definition of pressure in credible physics books. --Simian, 2005-09-29, 05:04 Z

Formula

Something's wierd about that formula. A vector divided by a scalar is still a vector. So the formular does indeed give a vector. (And it should also be expressed as a limit as A goes to 0, too. That avoids the problem where A is not flat, and so potentially the total resultant F on A is less than the fluid pressure times A.)

I think the problem is that we need to distinguish between the pressure exerted on the wall of a container, which is indeed a force (i.e. a vector, the limit of F/A), and the pressure inside the fluid, which is a scalar. They have the same numeric value (not to mention units), which is what is sometimes confusing, but are physically separate concepts. Noel (talk) 12:17, 6 Dec 2004 (UTC)

Oh, the right way to define the scalar pressure (at least for gasses, liquids are of course different) is to talk about it as a combination of the density of the gas (i.e. number of molecules per unit volume) together with its temperature (which is effectively a measure of the velocity of those particles), and bring in the gas laws. Noel (talk) 12:25, 6 Dec 2004 (UTC)

OK, fair warning - if someone doesn't like this, say so, because "shortly" I will edit the article to reflect these ideas. Noel (talk) 00:30, 16 Dec 2004 (UTC)

Noel:  Pressure (the magnitude of the normal force per unit area) is defined as a scalar, regardless of whether it's applied to a solid or fluid boundary, so these aren't physically separate concepts, as you speculated. I notice, after your above comments, it appears you never edited the article. --Simian, 2005-09-27, 19:13 Z

Pressure is a scalar. You can think of the definition as being F=AP, where A is the Vector area.--75.83.140.254 02:01, 10 December 2006 (UTC)

The definition should include differentials, to account for curved surfaces. Young and Freedman, (University Physics, 11th Ed. Pearson 2004.) offer the following definition: p = dF/dA, where p is pressure, dA is an infintesimal piece of the area of the surface, dF is a infintesimal part of the magnitude of the force normal to the surface. For force uniform over the area, the definition becomes p = F/A where F is the magnitude of the force normal to the surface.Leonhard Euler 08:56, 11 December 2006 (UTC)

Atmosphere

I removed the unqualified statement that use of the atm as a unit "should be avoided"; it's not a great unit for most scientific work, but there are times when it's a very good choice. For instance, in scuba diving it's quite a handy unit because it matches the usual baseline pressure, making it easy to calculate effects on gas volumes etc ('V2 = V1/P2' is simpler than 'V2 = V1*P1/P2'), and the "+10 metres = +1 atm" rule adds a simple relationship between depth and pressure. In this sort of application, precision is less important than simplicity of use. --Calair 01:09, 26 Dec 2004 (UTC)

The problem with the use of atmospheres as a unit of measure has nothing to do with precision, and only a little to do with ambiguity. It has to do with the fact that these are not, and cannot be, units in the International System of units, and are unlikely to ever be listed as units acceptable for use with SI or temporarily acceptable for use with SI.

For the approximation you discuss, the accuracy of the approximation is very much dependent upon factors such as whether this is sea water or salt water, and temperature. For that purpose, 0.01 MPa/m, or 100 m = 1 MPa, is just as good.

Some practical considerations about mental arithmetic: (1) The further the magnitude of your numbers is from 1, the more potential for error. (2) The more people have to work with fractions rather than whole numbers, the more potential for error. (3) The more operations you require someone to make, the more potential for error. (4) The more 'constants' that have to be remembered, the more potential for error.

As a simple example, let's suppose somebody wants to figure out the proportional volume change of his BCD as he goes from the surface to a depth of 30m (useful for gauging what will happen to his buoyancy as he descends).

Using atm/10 metre rule: depth = 30, 30/10 = 3 => pressure = 1+3=4 => proportional volume of BCD = 1/4. (I'm deliberately omitting units because that's how people generally conduct mental calculations, regardless of scientific correctness.) The only 'constant' that needs to be retrieved from memory is the 10 m/1 atm rule, and that only once.

Under SI: depth = 30. Pressure = 0.01 x 30 (or alternately, 30/100; either way, we have to retrieve a constant from memory at this point) = 0.3, plus atmospheric pressure 0.1 (retrieve a second constant from memory) = 0.4, so proportional volume = 0.1 (retrieve second constant again)/0.4 = 1/4.

Compare those two calculations. At every step of the way, the second is more prone to error. 30/10 is easier than 30/100 or 0.01 x 30; 1+3 is easier than 0.1 + 0.3; 1/4 is easier than 0.1/0.4. The first calculation only requires one 'constant' to be retrieved, once; the second requires two to be retrieved, one of them twice.

For a scientist working at the surface with a calculator, SI is wonderful. It's rigorously defined, it's 'scientifically correct', etc etc. As a professional scientist, I insist on working in SI and the many who don't are a source of perpetual annoyance to me. But when we're talking about non-professionals performing mental calculations in an unfamiliar environment, while undergoing physical exertion and quite possibly 'drunk' from nitrogen narcosis, the simpler method is to be favoured - even if it makes it harder for them to tell a scientist what they've done when they get home. --Calair 00:25, 28 Dec 2004 (UTC)

"Should be avoided" was a pretty mild way of putting it. Maybe I should come up with some stronger language before I reinstate it. Gene Nygaard 04:55, 27 Dec 2004 (UTC)

So what? Not everyone is a scientist. As long as there are significant communities of people for whom "atmosphere" is a useful, much-used, and well-understood unit, it's POV to call it "should be avoided". Noel (talk) 16:58, 27 Dec 2004 (UTC)

My wording could probably be cleaned up, but making clear what the standards-setters say does not violate NPOV. If it did, the mere classification into "SI units" and "other units" would also violate NPOV.

I would have absolutely no objection to noting that it's non-SI and so should be avoided in scientific use. But that objection applies equally to all units in the non-SI section; as such it should be stated at the beginning of the section, clearly applying to all, rather than as a note attached only to atm. As it was, that proscription was not stated with a context of "in scientific use", making it unjustifiably broad. --Calair 00:25, 28 Dec 2004 (UTC)

I notice also your failure to maintain the same laissez-faire attitude towards grams force. Or maybe that was just an oversight on your part? Gene Nygaard 17:25, 27 Dec 2004 (UTC)

I think you've misread my | edit there. As much as I loathe grams-force and such units, they are at least a legitimate unit of force and thus grams-force per cm^2 are a legitimate unit of pressure. The edit referred specifically to grams per cm^2 - not grams-force - and this usage is downright wrong. Not because it's not SI, but because it's not even dimensionally correct; grams and grams-force are not the same thing. --Calair 00:25, 28 Dec 2004 (UTC)

If you want to say that it's not an SI unit, and use of atmosphere in scientific settings is therefore non desirable (I see it used in engineering stuff all the time, e.g. NASA spacecraft documentation), I have no problem with that. As to the "grams force", I have no idea what you're talking about. Are you confusing me with someone else? Noel (talk) 17:46, 27 Dec 2004 (UTC)

I mainly want to distinguish two different uses: a standard atmosphere as a constant, which is acceptable for use with SI, versus a standard atmosphere as a unit of measure, which is not. Perhaps the "standard model of the atmosphere" (not sure if that's the best name for this more involved concept) needs to be distinguished as well?

Yes, it was Calair, not you, who took out my comment about atmospheres being unacceptable, while not making a similar change to my comments about the 'g cm^-2' units (often seen as "kg/cm²" pressure gauges) no longer being acceptable.

Curiously, the same Calair who took out my incorrect usage comment was the same one who inserted language about 'g·cm²', saying that "this usage is incorrect and should be avoided." After I clarified this, Calair left my statement untouched: "those formerly acceptable grams force are not a part of the modern SI and should be avoided." That was, however, a more detailed explanation than my statement about the use of the atmosphere as a unit of measure, so I concur in the need to revise my statement in that regard. Gene Nygaard 18:11, 27 Dec 2004 (UTC)

I left it untouched because it's a busy time of year and I got distracted. Your statement does need to be clarified, because the problem with "g/cm^2" is not that "grams-force" aren't SI but that "grams" are not "grams-force"; the second half is correct but non-sequitur.

My two edits are better seen as unrelated. The point of the 'atm' one was that although atms are not a SI unit of pressure, there are occasions when non-SI units are appropriate. The point of the other was that "g/cm^2" are not a legitimate unit for pressure at all, because "g" is not a unit of force. I would not have made the same objection to "grams-force/cm^2"; I don't like those units at all, but at least they're not outright *wrong*. --Calair 00:25, 28 Dec 2004 (UTC)

That argument applies equally to pounds-force, tons-force, and the like. Make the same point about them, if you make it about grams-force (note that you specifically disclaimed the fact that grams-force are not SI as a reason for objection, so there is absolutely no other difference involved here). Gene Nygaard 06:52, 17 Jan 2005 (UTC)

Actually, there is a difference - claiming that "pounds are not a unit of force" is vastly more likely to trigger time-wasting arguments than making the same claim about grams. Further, since I have much more use for and interest in metric units than pounds & derivatives, I'm not the person to correct the latter. If somebody else wants to do it, great; in the meantime, better to correct some of the article than none of it.--Calair 12:06, 18 Jan 2005 (UTC)

Stagnation pressure

Stagnation pressure' is the pressure a fluid exerts when it is motionless... although a fluid moving at higher speed will have a lower static pressure, it may have a higher stagnation pressure

Talking about the stagnation pressure of a moving fluid is very confusing when we've just defined that as the pressure it exerts when it is motionless - is it possible to clarify the definition a bit here? --Calair 22:49, 12 Mar 2005 (UTC)

Problems with example

A tow truck can exert a vast force in pulling a car without causing damage. However, a baseball bat directed against a certain part of car is likely to damage the car. That is because the focus of the bat exerts more pressure on that specific part of the car.

I don't think this is a good example. For starters, the wording implies (although doesn't actually state) that the towing force is greater than that inflicted by the bat. Some very rough calculations:

Baseball bat: ~ 1 kg. Speed of swung bat: ~ 50 mph ~ 20 m/s (using figures for an untrained 12yo with a smaller bat [1]) Stopping distance: say, 0.02m (~1-inch dent.)

Assuming force during impact is proportional to indentation (i.e. y = -ky, y being indentation distance): from initial impact to stopping, y = a sin(bt) for some a & b, t being time from initial impact. At stopping point, y' = 0, so a = 0.02m. y' = ab cos(bt) = 0.02m*b*cos(bt) At t=0, y'=20 m/s & cos(bt)=1 so b = (20 m/s)/0.02m = 1000/s. y=-0.02m*b²*sin(bt) At stopping point, sin(bt)=1 therefore y=-0.02m*(1000/s)² = -20000 m/s² so peak impact force ~ 20000 m/s² * 1 kg = 20000 N.

Mass of big car: ~ 3000 kg. Jeep Grand Cherokee, towing ~3000 kg load: 0 to 30 mph (~ 13 m/s) in 6.4 sec [2] (I couldn't find stats for tow truck acceleration, but I doubt they're much faster.) so mean acceleration ~ 2 m/s² so mean towing force during acceleration ~ 6000 N. (Peak forces will be somewhat higher, since acceleration isn't constant throughout takeoff.)

Getting past that, this is still comparing apples to oranges. If you're trying to dent somebody's car with a baseball bat, you're going for panels and the like; the towbar is rather more solidly built. Further, denting a panel is about bending, while towing is mostly straight compression/tension. If we want to show people the effects of a difference in pressure, we really need to apply both pressures to the same target in the same sort of way.

The classic examples I always heard were "elephant standing on floor vs. person in stiletto heels on same floor" and "thumb pressing on corkboard vs point of thumbtack pressing on corkboard" - I think either of these would be preferable. --Calair 01:57, 13 Apr 2005 (UTC)

Admin advice requested. Continual reversions - no discussions

Im having trouble with an unregisterd user continually reverting with no discussions,. Using a variey of URLs. Any Admin advice please?--Light current 15:04, 20 October 2005 (UTC)

1. (cur) (last) 15:51, 20 October 2005 139.169.2.162 (rv edits by Light current to last version by 67.50.187.18)
2. (cur) (last) 15:30, 20 October 2005 Light current (reinstate improvement)
3. (cur) (last) 07:00, 19 October 2005 67.50.187.18 (rv edits by Light current, changes don't make sense and degrade article)
4. (cur) (last) 06:29, 19 October 2005 Light current (rvv)
5. (cur) (last) 05:08, 19 October 2005 67.50.186.118 (rv all changes by Light current to last version by Simian except for one new heading)
6. (cur) (last) 04:22, 19 October 2005 Light current (→Hydrostatic pressure - mass not weigth)
7. (cur) (last) 04:20, 19 October 2005 Light current (explain g)
8. (cur) (last) 04:11, 19 October 2005 Light current (→Hydrostatic pressure - put g back)
9. (cur) (last) 03:59, 19 October 2005 Light current (→Hydrostatic pressure - pressure = depth* density)
10. (cur) (last) 03:57, 19 October 2005 Light current (→Scalar quantities - rm xs hdg)
11. (cur) (last) 03:54, 19 October 2005 Light current (reordered paras+hdgs)

I'm no admin, but lack of discussion is a two-way street. I notice this is your first posting on this talk page, and even now you offer no explanation of your extensive rewriting of the page. Let's start with the basics, okay? What are you trying to accomplish?

Ever hear of the "clean-hands doctrine"? Gene Nygaard 15:26, 20 October 2005 (UTC)

I thought it obvious. Im trying to establish a clean, ordered, easy to read, professoinal, accurate looking page like they all should be OK?--Light current 15:51, 20 October 2005 (UTC)

Also youll notice thyat nothing has been done since the start of this month on the page- I though it was time for some fresh eye to look it over. Call me a new broom if you like!--Light current 15:57, 20 October 2005 (UTC)

THis person maybe a sock of someone who has a particular grudge against me.--Light current 16:12, 20 October 2005 (UTC)

Why'd you duplicate the p = f/A equation and surrounding text? Pfalstad 20:47, 20 October 2005 (UTC)

Because I kept getting reverted when I did more major change. I will be removed when the reversion problem is resolved--Light current 21:54, 20 October 2005 (UTC)

I may have missed something in the change history, but I don't see anything very sweeping in Light current's changes. AFAICT most of them are minor structural changes without actually adding or deleting much material at all. For major changes, sure, it's courteous to discuss them in advance. But for little tweaks like this, there's no need for the editor to start defending them until somebody else raises an objection. Otherwise we'd spend half our time justifying what we're about to do instead of doing it.

Overall, I think the changes are a slight improvement to the structure, and I don't see any justification for auto reverts without discussion. --Calair 23:56, 20 October 2005 (UTC)

Unit of Pressure: WC

The unit of pressure WC needs to be added to the list of units. This is commonly used to measure natural gas line pressure.

27.68" water column = 1 PSI

LexieM 21:53, 30 January 2006 (UTC)

'Inches of water' are listed in the Units section (under 'manometric', near the end). I think this is the same thing, but I've noted the abbreviation in the discussion of manometric pressure. Apologies for the multiple edits, kept getting things wrong today. --Calair 23:11, 30 January 2006 (UTC)

Appropriate precision for g

As per discussion at gee, the difference in centripetal effects between equator & poles causes a variation of about 0.034m/s² in perceived gravity over the Earth's surface at sea level; the effects of the equatorial bulge bring this up to about 0.052 m/s^2, so we should not be offering two decimal places of precision. When one adds in non-sea-level terrain, even "9.8 m/s²" starts to look like excessive precision. --Calair 22:57, 31 January 2006 (UTC)

It is also 9.8 m/s² atop Mount Chimborazo, the highest mountain on Earth in both ways relevant here, and 9.8 m/s² at the Dead Sea, so your "at sea level" is exactly the same kind of excessive precision, just in words rather than in numbers. Gene Nygaard 02:50, 1 February 2006 (UTC)

I agree with your revert, based on those numbers, but stipulating "at sea level" most certainly is not 'excessive precision'. In fact, it's the opposite of excessive precision - it's an unnecessarily weak statement (but a true one everywhere in the world), whereas the "9.81 m/s²" statement was an unjustifiably strong one that is false in some parts of the world. --Calair 03:47, 1 February 2006 (UTC)

5. Why is it possible to lie on a bed of nails and not be pierced?

asap ..

Pascals to psi

That 10^-6 should be 10^-4.

No, the value given is correct (at least to the order of magnitude, I haven't checked past the first sig fig); note that it's 145 x 10^-6, not 1.45 x 10^-6. The table is using engineering notation, which keeps exponents to multiples of 3. I'm not very fond of engineering notation myself, but it's not actually wrong. --Calair 02:33, 24 May 2006 (UTC)

Hi! I found that in units table there is like: 1 psi = 6,894.76 Pa maybe it should be like this: 1 psi = 6 894.76 Pa ?

I'm guessing from your IP that you're from Estonia? Different countries have different formats for writing out numbers. In the USA and Australia (and I think the UK too), when writing a large number (say, sixty-five million, eight hundred and forty-three thousand, two hundred and five, and seventeen hundredths), it's normal to write it with commas separating the thousands, millions, etc: "65,843,205.17". In some countries - this article tells me Sweden is one of them, and it looks as if Estonia is too - spaces are used instead of commas, so the same number would be written "65 843 205.17". And in yet others, e.g. Germany, periods are used as thousands separators and a comma for the decimal place: "65.843.205,17" (which can be very confusing if you get a number like "13,205" or "13.205" and don't know which convention is used).

AFAIK, the first format is most common in the English-speaking world so it's probably the best choice for an English-language article. From a technical viewpoint, it also has the advantage that using a comma keeps the number as a single 'word' that isn't at risk of being broken up by computer formatting - you're not likely to end up with the '6' at the end of one line and the '894.76' somewhere else on the page. --Calair 02:19, 18 October 2006 (UTC)

"Gage" v.s. "Gauge" Pressure (Spelling)

Instruments that measure pressure are called "gauges." Measuring pressure with respect to atmospheric pressure is "gage pressure". There are plenty of examples where Americans incorrectly spell it "gauge pressure" and where some British users spell it "gauge pressure." However, by far the most important criteria is how the pressure measuring industry spells it. These are the people who make pressure transducers and other instruments. All the biggest and most dominant manufacturers spell it "gage pressure" and doing otherwise is simply incorrect. Here's a list of some notable industry insiders (and links to a Web page with the proper usage):

• Omega Engineering (a huge reseller)
  
• Honeywell-Sensotec-SenSym
  
• Thorsten Klose (a German-based seller with an English-language Web site)
  
• Repcon (an Italy-based seller with an Italian-language Web site)
  
• Davis Instruments (a seller)
  
• Fluke Corporation
  

I've got sixty linear feet of engineering catalogs (all indexed on Roledex cards) and probably one-and-a-half feet of it are dedicated to pressure sensors, gauges, and transducers. All of them use the term "gage pressure." I'm sure someone can always find Web sites (where everyone can look like an expert) that spell it "gauge" pressure (I'll bet that automotive-related, grease-monkey sites are rife with the error) but that is not the spelling the vast bulk of the pressure measuring industry (the experts) uses. Just the weight of such colossal companies as Omega Engineering and Honeywell-Sensotec-SenSym alone (both of which use "gage pressure") should be enough critical mass on this issue of spelling to settle the issue right there. Spelling it "gauge pressure" is simply a weird, incorrect spelling and Wikipedia shouldn't be leading people astray with it. Greg L 06:42, 5 December 2006 (UTC)

Careful of confirmation bias there. Most of the same manufacturers you cite - including the two 'critical mass' ones also make frequent use of 'gauge pressure': Omega Engineering[3][4][5], Honeywell-Sensotec-SenSym[6][7][8][9], Sensata[10][11][12], Davis[13][14][15]

As for the Thorsten Klose site, the only usage I can find for 'gage pressure' there seems to be a submission sent in by a user rather than the company's own material; in any case, the surrounding material is obviously not a shining example of good English usage. ("More advanced sample programming let's you control also the filter and so, the more you blow, the more higher frequency you add, just like in real life. If you search on web about resources and tips about BC, you'll learn in how many different way you can use it...")

Given that Omega and Honeywell-Sensotec-SenSym are indeed colossal companies in this field, their frequent usage of 'gauge pressure' should be enough to indicate that it is an accepted spelling in the industry. As per Wikipedia:Manual_of_Style#Disputes_over_style_issues, in situations like this the version originally used in the article should be kept. --Calair 07:44, 5 December 2006 (UTC)

The use of "gauge pressure" seems to be a byproduct of less rigorous proof-checking by Web masters. You won't find "gauge pressure" in any of the above companies big-book catalogs. And if you look at the companies' more time-tested Web pages such as Honeywell's FAQ page, you will get the proper spelling. Also, if you go to the Fluke product search site, "gauge pressure" returns nothing and, of course, "gage pressure" gives results for all their gage pressure products. One can Google on "gauge pressure" and get lots of hits because it is one of the most common misspellings in English. The really sad part is if you Google on "gauge pressure" + "definition," some of the hits are robot sites that simply parrot this article. You can walk into any automotive supply store and if you ask what the "g" in psig means, some "Mr. Goodwrench"-looking manager will verbally say it stands for "gauge". The average fellow will assume the word is spelled like "pressure gauge." It's a phenomenon much like the pronunciation of "giga" (as in gigawatts or gigabytes). Originally (before the 1990s), it took its pronunciation from its root meaning and sounded like "gigantic." Once the average Joe read it over and over in computer magazines but never heard the word in use, they assume it's pronounced with a hard "G."

As with "giga," one could argue that improper usage makes it acceptable. But in this mater, you can't hid behind the apron strings of "Style issues." That's tantamount to saying "it was originally incomplete information and Wikipedia's policy as disclosed in their Manual of Style says it can remain as originally written." Nice try; but you know better. Making a flat declaration in Wikipedia that it is spelled "gauge pressure" (period) is intellectually dishonest and isn't stating the whole truth. It is also impermissible to diminish the truth about the "gage" spelling by mentioning it only parenthetically like "(oh, it's also sometimes spelled 'gage pressure)"; this too is being dishonest with the facts. At the very least, the reader must know the true facts about the spelling and how the pressure measuring industry often uses "gage pressure." Greg L 19:37, 5 December 2006 (UTC)

Please familiarise yourself with WP:AGF before making accusations of 'intellectual dishonesty'; that sort of talk is not productive. I picked the Honeywell and Omega sites because I thought we both viewed these as credible sources, but if they aren't satisfactory I can offer more - none of them Wikipedia mirror sites or auto mechanics.

(Note that a few of the hits on 'gauge pressure' listed below are from outside the usage we're discussing - things like 'wave gauge, pressure type' or 'strain gauge pressure transducer'. I haven't checked every last hit, but I've looked through enough to satisfy myself that these false hits aren't numerous enough to make much difference.)

Sites that consistently use 'gauge pressure', as far as I can determine: Eric Weisstein's ScienceWorld[16], the UK's National Physical Laboratory[17] (including the UK's National Pressure Standards), Science magazine[18][19] (subscription required) and Encarta[20]. IUPAC's 'Glossary of Atmospheric Chemistry Terms also uses 'gauge pressure'.

Reputable sources that use both (and I stopped for reasons of time and space, not because I ran out of examples - more available on request) include the US Army Corps of Engineers (18 hits for 'gauge pressure' vs 13 hits for 'gage pressure'), the NOAA (39 'gauge pressure' vs [8 'gage pressure']), publications of the American Chemical Society (103 'gauge' vs 169 'gage', and in particular the American Physical Society (123 'gauge pressure' vs only 4 'gage pressure' within link.aps.org). The APS is the world's largest English-language physical society, and frequent use in peer-reviewed APS publications should in itself be enough to confirm that 'gauge pressure' is an established usage, particularly when backed up by other reputable scientific organisations such as the ACS and NPL.

Still, if it'd be acceptable to you, I'd be happy to go for a third opinion. --Calair 00:37, 6 December 2006 (UTC)

I have both a 1998 and a 2006 Thomas Register (the multi-volume resource for buying). The 2006 will be the last print version ever. I checked in both and indeed, there are some companies that advertise "gauge pressure." By far however, most use "gage pressure" and this is observation is also borne out by the Web sites I referenced earlier. My old catalog set goes back decades and companies like Sensotec and SenSym (I specified both of their products earlier in my engineering career) were ultimately bought up by Honeywell. All those catalogs always used "gage pressure."

Nowadays, the easiest way to buy small amounts of pressure transducers is through Omega Engineering. They're the "Sears Roebuck" of engineering supply. And if you look in their indexes of their hard-cover catalogs, the spelling is always "gage pressure." Now I can see—as you've found out—that on the Web, "gauge pressure" sneaked into some their individual Web pages featuring a specific product of someone's. Honeywell and Fluke are more consistent. The translation to the Web introduces a whole new opportunity for error. Entire Web pages are now reviewed and approved by clerical-types in the manufacturer's front office. But when expensive catalogs are published, the proof-checking is more thorough and drafts are typically reviewed by Engineering. Fluke is a classy organization and their Web sites should be applauded for having no (or nearly none) goofs. As I stated above, Honeywell's FAQ sheet consistently spells it "gage pressure" and Fluke's entire Web site does too. These two are the dominate players in the industry.

There is a real, practical advantage for "gage pressure" and I supposed this is the underlying reason it's spelled the way it is: since "gauge" is the spelling for the noun referring to the measuring instruments, spelling it "gage pressure" avoids ambiguity as to what one is referring to. I can see for myself when I Google on the various spellings that there are seemingly legitimate sources that use "gauge pressure." Some do it on purpose. Apparently, it is more common in the U.K. And one could count eighteen of examples of "gauge pressure" here and twelve instances there and quickly run out of fingers and toes to count them all on; the Web multiplies common misconceptions and folk lore very, very quickly. But clearly, the dominant usage by the big manufacturers (people who ought to know) in their formal publications is "gage pressure."

This doesn't have to be an all-or-nothing affair with regard to the spelling. But the Wikipedia article should accurately and honestly address the issue of "gage pressure" and "gauge pressure." Most world-wide manufactures of pressure-measuring instrumentation use the term "gage pressure" in their most official publications and FAQ sheets. Honeywell-Sensotec-SenSym does and so does Fluke (which bought-up a bunch of companies themselves). Opening the hard-copy version of Thomas Register reveals the same. "Gage pressure" has historically been by far the dominate spelling for the industry and continues to be to this date. Any attempt to address the issue of spelling the term in this article should acknowledge these facts. Greg L 03:04, 6 December 2006 (UTC)

"since "gauge" is the spelling for the noun referring to the measuring instruments" - certainly the more common spelling in my experience, but not a clear-cut distinction. 'Gage' is also used in this sense now and then, enough that the American Heritage Dictionary treats it as just a variant spelling of 'gauge'; 'gauge' seems to be the majority usage for measuring instruments, but there are enough companies out there selling 'gages' (for instance, the Meyer Gage Company that 'gage pressure' is still ambiguous. Given inevitable human sloppiness and how often the two terms show up in the same contexts, I suspect it always will be.

Certainly the big manufacturers ought to know the correct spelling - but so should the National Physical Laboratory, and researchers publishing with organisations like the APS and ACS (not to mention their editors and publishers), and as best I can tell 'gauge pressure' is the more common usage in scientific publications of that sort. It's hard to look at those and say that 'gauge pressure' is not a common and widely-accepted usage, and given the choice between two such usages the one first introduced to the article should generally prevail.

I would, in principle, support saying something like "'gage pressure' is more commonly used by manufacturers, 'gauge pressure' by physical scientists" in the article. However, I'm not sure how to do it without drifting into original research - IMHO the sort of arguments we've produced here are acceptable for resolving a stylistic issue on a talk page, but have far too much synthesis and interpretation (on both sides) to be adequate support for claims of fact within article space.

And all that said... I have nothing against "gage pressure", and if that had been the first version I would've been happy to leave it that way. My only objection here is on the principle that articles should remain stable on such points unless there's a strong reason to change (the essence of Wikipedia:Manual_of_Style#Disputes_over_style_issues, and it doesn't seem to me that either the disparities in usage or the effect on ambiguity are enough to constitute a strong reason.

But at this point I'm inclined to just ignore the MoS, on the basis that both of us probably have more useful things we could be doing on Wikipedia (or off it) than wrangling over this issue. If nobody else wants to make an issue of it, I'd be willing - in a non-precedent-setting way - to accept something like "...gage pressure (also spelled 'gauge pressure')" followed by consistent 'gage pressure', in this and related articles. I'm not entirely happy about changing the article spelling, but life's too short. --Calair 04:41, 6 December 2006 (UTC) - struck out as no longer relevant since another editor has objected to it. --Calair 03:18, 11 December 2006 (UTC)

If I may offer my opinion: since this is an article on pressure, which has far more scope in readership than those interested in buying a pressure gauge to measure gauge pressure from industrial producers, then I think we should go along with IUPAC, APS, National Physical Lab, etc and their usage of gauge pressure. LeBofSportif 13:09, 8 December 2006 (UTC)

Your listing of various organizations that use "gauge pressure" and then using the term "etc" at the end of the list could lead one to falsely conclude that the great weight of official organizations exclusively use that particular spelling. But if you search around, one will find that organizations sometimes use both spellings. And of course, a proponent of the spelling "gage pressure" can shoot back with their own list of very impressive organizations and companies. One can quickly get themselves into a "battle of citations" (who's organizations are more prestigious, or who has the biggest list). For instance, this paper, Recommended Use of SI Units in the Nuclear Rocket Engine Program (1.2 MB PDF) was published by rocket scientists at Los Alamos Scientific Laboratory and is available on a Web site owned by the Federation of American Scientists. It's a white paper governing the proper formating of pressures, temperatures, masses, etc. in the program's documentation. In it, they say it's written "gage" and the paper further specifies what Calair wrote earlier about: how "gage" should be in parenthesis where practical (rather than tacked onto the end of an SI unit symbol without a delimiter of any sort). Hey, that's all pretty impressive credentials isn't it? It's an older paper; from the good ol' days when, perhaps, people were more rigorous about writing scientific stuff. But does the fact that I can come up with really smart rocket scientists who spelled it "gage pressure" mean that's the way it should be spelled? I don't think so. The best source for the proper terminology and spelling is to go to the experts: the pressure measuring industry and their engineers. From most manufacturers —particularly the bigger ones — all you'll find in it your big fat catalogs is "gage pressure." Greg L 20:45, 8 December 2006 (UTC)

Firstly, Greg L, you are not neutral on this sort of matter - your rant in Talk:Caesium (yes, caesium) goes to show that, where you state "Wikipedia ... should use American english. Period". Well - that is just not wikipedia policy, but you have made it clear that it is your opinion, so perhaps you are not the best placed to decide between gage and gauge, given this bias. Secondly, I will retract my "etc" if you like. I suggest we take our lead from international organisations who we can consider to have had these disputes already (eg IUPAC) or from relevant national standards institutes, eg NIST (gauge beats gage on google search) and UK NPL (gauge beats gage on google search). Consider this NPL education link too: [21]. Or take our lead from renowned centres of research: eg MIT (gauge beats gage 156:32). I do not think that american industry catalogues are the source to follow. And the precedent in this article, and wikipedia, is gauge. You have not provided good reason to switch from that. LeBofSportif 11:24, 9 December 2006 (UTC)

I didn't know that underlying this argument was that you saw this as another one of those "British spelling booboos" that has you all animated. Well, if you want to make it a "country" thing, I could always then cite the following:

• Thorsten Klose (a German-based seller with an English-language Web site)
  
• Repcon (an Italy-based seller with an Italian-language Web site)
  

I'm sure you can come up with your own list of other countries’ sites that use "gauge pressure." (New Zealand?). As I stated before, one can quickly get themselves into a "battle of citations" (who's organizations are more prestigious, or who has the biggest list). Notwithstanding that you seem anxious to make this another British vs. American-English spelling "thing", the simple reality is that the largest players in the pressure-measuring industry predominately use "gage pressure" (Honeywell-Sensotec’s FAQ page and Fluke Corporation’s product search page) and that many organizations and resellers world-wide follow this convention. In light of this, the existing wording, which says "(also often spelled 'gauge pressure')" faithfully states the facts, properly lets the reader know there are alternative spellings, and strikes a much better balance with the reality of the situation than what was in the article before. Greg L 17:11, 9 December 2006 (UTC)

I suspect we're not going to reach consensus without additional input, so I've posted a RfC.--Calair 03:18, 11 December 2006 (UTC)

So what's wrong with what the article currently says, which is "gage (sometimes spelled gauge)"? linas 05:13, 11 December 2006 (UTC)

I don't think anybody is opposed to the article acknowledging both spellings. The issue is which of them should be used as the default here and in related articles. Originally the article used 'gauge' throughout, but recent edits have changed this to 'gage'.

WP:MOS states that "when either of two styles is acceptable, it is inappropriate for a Wikipedia editor to change from one style to another unless there is some substantial reason for the change.... If in doubt, defer to the style used by the first major contributor." (See also Wikipedia:Requests for arbitration/Jguk.)

My position is that both 'gauge' and 'gage' are widely-used and reputable spellings (see discussion above for the gory details), therefore there was not a substantial reason for change, therefore the original version ('gauge') should be used with a "sometimes spelled 'gage'" in there somewhere. --Calair 06:25, 11 December 2006 (UTC)

I agree, and the page needs to be changed back. Gene Nygaard 06:31, 11 December 2006 (UTC)