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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
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)
The usage on the page is inconsistent. Then shouldn't it be pV=nRT? I've always seen P used for pressure in the ideal gas law. I know that P is phosphorus, but in every chem book I've ever seen, it seems that P is used for pressure, too. I think the page needs to be changed to "(symbol: 'p' or 'P')" in order to be correct. Any comments about this? Sushilover2000 ( talk) 15:13, 17 November 2008 (UTC)
I'm in mechanical engineering specializing in fluids and I can say that I've seen no adherence to any convention between sources. It's entirely context-driven, ie left to the discretion of the author to not confuse the reader. To say that big P is reserved for power is simply wrong as I can pull a dozen sources on fluid mechanics in five minutes that directly contradict that. I honestly don't know why so much fuss is being made over whether the p is capitalized or not anyway. The p represents pressure when the author is talking about pressure, regardless of capitalization. Though I do think the p sometimes P bit is wordy and unnecessary since stating the letter p is use for pressure seems sufficient. In my experience there is very little convention for capitalization on many variables. I've seen i and I for current, p and P for power, l and L for length. Iron_Engineer ( talk) 18:08, 1 July 2009 (UTC)
I added a reference to the IUPAC standard (lower-case p), and moved the footnote into the body of the text. I first came to this article to figure out if pressure should be p or P, so I expect some others will be looking for that information. The lack of consensus, which was conveyed by the footnote, is worth including in the body of the article (I think). Christopher King ( talk) 13:30, 20 December 2015 (UTC)
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.
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
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 i still dont get it
There is room for improvement here. I hope to get to making edits soon, but will put some thoughts here and try for some feedback first. Maybe one of you is better at this stuff than I am anyway. Here are some areas I hope to address:
Seanmichaelmcintyre ( talk) 19:05, 25 April 2013 (UTC)
The section about pressure as potential energy doesn't hold true for incompressible liquids. Take a hydraulic cylinder. YOu can increase the pressure but without a change in volume. Therefore no work in there will be no work out. — Preceding unsigned comment added by 68.47.28.48 ( talk) 03:32, 18 July 2020 (UTC)
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)
Somebody has sabotaged the formula. 68.149.173.141 ( talk) 02:24, 14 January 2010 (UTC)
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)
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)
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)
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)
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)
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)
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)
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)
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)
Hey what about 'ksca'? The unit 'kilogram per square centimeter absolute' is used sometimes too. I had a hell lot of trouble finding it's expansion as its more usual form kg/cm2 is so common and I could not immediately make the connection (though I was trying to see if anything fits in as with 'psi' and 'pounds per square inch', so very dumb of me!). Elncid ( talk) 11:21, 16 January 2008 (UTC)
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)
asap .. The only thing to manage is to lie on the bed such that the pressure on all the nails is equal. In each and every surface there are some irregularities that interlock , thus a type of surface is formed by the nails.-- 115.240.129.38 ( talk) 16:21, 6 September 2009 (UTC)
That 10^-6 should be 10^-4.
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 ?
mga tae kc ung pressure n nagsamasama upang makbuo ng isang boung malikng pressure —Preceding unsigned comment added by 203.111.234.59 ( talk) 09:50, 16 January 2009 (UTC)
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):
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)
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)
So what's wrong with what the article currently says, which is "gage (sometimes spelled gauge)"? linas 05:13, 11 December 2006 (UTC)
Why is this (important) question in metrology the second section of the article? The definition of pressure is the same, whether its is measuered ga(u)ge or absolute. Gauge pressure and gage pressure should not redirect here. Physchim62 (talk) 13:22, 11 December 2006 (UTC)
Rather than Nick Y's ill-informed rampant speculation about some "error" caused by "spell-checkers" in the last "10-15 years", let's just look at what the experts in some reliable sources have to say about that. Here's Webster's Third New International Dictionary, Unabridges, 1961:
Note that for definition 3, the use of this variant is not limited to a particular definition of the word. Nor is it limited to a particular part of speech. This variant is one used for any of the various meanings of gauge, whether used as a noun, as a verb, as an adjctive, or whatever.
And, by the way, for the math-challenged among you, 1961 is more than "10-15 years ago." Gene Nygaard 22:19, 12 December 2006 (UTC)
Webster's Third, 1961:
Note that there is no entry for "gage pressure". Gene Nygaard 22:43, 12 December 2006 (UTC)
All that really matters is the etymology. Webster's Third, 1961:
You might want to go check out Middle English, to see if this likely results from the "use of spell-checkers in the past 10-15 years"! It turned into Early Modern English over 600 years ago. What do you have to say now, Nick Y? Gene Nygaard 22:49, 12 December 2006 (UTC)
This section intentionally blank, and likely to remain so.
I think you need to chill a bit, ...Dude. As I stated when I entered this thread I am an impartial editor. I think you might infer from that that I am not claiming to be an expert. My qualifications or age aren't particularly relevant except being a level headed editor. My conclusion was that we should use gauge first and reference gage secondarily based on the British evidence provided by Greg L. I think we need to hash out the current and historical usage of both words. This includes scientific and engineering usage and not just dictionary definition. The Webster's 3rd 1961 definition seems to validate your point very well. Thank you for bringing this to our collective attention. With the additional references from the past it seems clear that "gauge" and "gage" have been interchangeable in this usage in the US in some people's eyes for quite a while if not forever. It remains true however that gage is very heavily used in the US scientific and engineering fields and the use of gauge is frowned upon by some. It is also true that the use of gage appears to be declining. I still believe that this phenomenon is due to my spell checker hypothesis despite whether gauge is an acceptable interchangeable spelling. It simply looks more familiar to most people. But all of that is irrelevant. For the purpose of this article I would say that "gauge (also gage)" or perhaps "gauge (also gage in US English)" will suffice. I think we are done here? Peace-- Nick Y. 18:46, 13 December 2006 (UTC)
Feel free to add other references to those subsections if you like, Nick or anybody else. Just stop the wild speculation that has generally proved to be false. Here, for what it is worth, are some results of Google searches. Gene Nygaard 16:09, 14 December 2006 (UTC)
hits | |
---|---|
"pressure gauge" -Wikipedia | 1,240,000 |
"pressure gage" -Wikipedia | 195,200 |
"gauge pressure" -Wikipedia | 383,000 |
"gage pressure" -Wikipedia | 83,300 |
gauge psig | 480,000 |
gage psig | 139,000 |
gauge kPa OR MPa | 1,000,000 |
gage kPa OR MPa | 337,000 |
site:xxx | |||||||
---|---|---|---|---|---|---|---|
.org | .edu | .mil | .uk | .ca | .au | nist.gov | |
"pressure gauge" | 304,000 | 1,250,000 | 9,390 | 114,000 | 32,100 | 38,500 | 163 |
"pressure gage" | 27,600 | 198,000 | 570 | 1,080 | 1,150 | 337 | 58 |
"gauge pressure" | 59,900 | 391,000 | 205 | 902 | 686 | 692 | 67 |
"gage pressure" | 12,200 | 84,200 | 231 | 435 | 289 | 81 | 38 |
Please allow me to say that I am by no means an expert in this field. Rather just a student who has studied gauge pressure in General Physics. I have nothing but for respect for anyone entrenched in this field but I just wanted to offer an opinon from the side of what's being taught in schools. "University Physics" by Young and Freedman, volumes I and II refer to the spelling of gauge pressure and not gage pressure. Also from what I've understood it's called gauge pressure because it's measure on a gauge excluding atmospheric pressure, hence that's where the spelling comes from. Further I believe the more common spelling of gauge has been established by
Gene Nygaard that the world overwhelmingly uses the spelling gauge pressure. As such I vote to support gauge pressure--
Robert Stone, Jr.
03:47, 5 January 2007 (UTC)
It seems "gauge pressure" is the consensus here --- Safemariner 04:57, 8 January 2007 (UTC)
[sigh...] Where to begin? I am a humble copy editor who came across this article because it was tagged with {{copyedit}}. The issue was an inconsistency in the spelling of the word gauge (also spelled gage)—or is it gage (also spelled gauge)? Words cannot express my reluctance to revisit this debate, which I thought was resolved in January 2007. Here is what I will do:
I hope this will address the copy edit issue, and respect the consensus of the editors involved. Cheers. Braincricket ( talk) 09:22, 4 January 2012 (UTC)
To unnecessarily (and probably unwisely) re-visit a bitter (and long...I ran out of popcorn!) debate, I just felt I had to add my own personal observation that it always strikes me as foolish when people act as if a change in a words pronunciation or spelling was desecrating thousands of years of history written in stone, when language has changed constantly throughout history (and will continue to do so), and when "official spellings" as such were non-existent or unknown up until quite recently. At some point, people decided they would sit down and freeze language into stone, which I think is a futile attempt doomed to failure, and whenever certain people see other people using the "official" language "incorrectly", they form a mob and break out the torches. It's even worse in cases like this where they disagree on what the official spelling even is. Granted, in fields of scientific endeavor, some terms must be made constant and uniform, but in this particular case, does it really matter that much whether it's spelled "gage" or "gauge"? You might loose a little precision, but the while thing isn't worth starting a jihad over, especially since it's unlikely that proponents of one variant will ever change the way people in another country spell the word. I think it's wiser to simply educate people if they see "gauge pressure" or "gage pressure", they may well mean the same thing, and it's up to them to be aware of this and use common sense. Most people dealing with this sort of thing ought to be intelligent enough to muddle through a small difference in spelling if they know that it could mean either thing. Personally, I prefer "gauge", for the simple reason that I consider "gage" to be ugly (a dumb reason, yes). That's also why I use "grey" instead of "gray", even though it's "incorrect" to do so. Unless you live in the UK, anyway.
One question though, I'd genuinely like to know...one sentence in the above debate seems to be saying that "gage" is pronounced differently than "gauge". Is this true? He says that
"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."
So "gage" is pronounced "jahy-juh" then? That's certainly a education for me. If it's not true, I fail to see what the relevance is...is the auto store man supposed to spell it out for him? How are two words spelled differently and pronounced the same the same thing as a word that was simply misread and entered public consciousness in a way it wasn't originally intended to do. A "gigawatt" is a "gigawatt", regardless of how you pronounce it, while the whole point of the complaining side of this debate is that that "gauge" and "gage" have two different meanings, in spite of being pronounced the same. I fail to see any real parallel there.
As a last note, for what it's worth, I was taught at some place or other that "gage" is simply an American simplification of the older British term "gauge", but both are considered correct spellings in the US (of course, in that context it was referring to "gauges" such as instruments). I believe I looked it up, because the first time I saw "gage" written out, I assumed it was a spelling error, because I'd never seen it spelled that way before. .45Colt 07:48, 19 August 2015 (UTC)
I deleted the Biology part since it was just vandalism by someone who was trying to be funny. Ranmamaru 06:29, 11 January 2007 (UTC)
ok so volume of a liquid has to be conserved (given it is incompressible, non viscous blah blah) but why should the force per unit area be conserved and be the same in all directions? Basically if I just model everything as volume conservation and simply try and say that the liquid "en mass" will try to attain a level of minimal potential energy, I still end up with the same results. However to make the assumption that dF/dA is conserved seems off beat to me. —The preceding unsigned comment was added by 220.227.207.194 ( talk) 09:28, 5 March 2007 (UTC).
ans. analytically u can consider pressure on a liquid molecule as a contact push due to vertical( upward )layer of molecules constantly acting on it. hence it is a summation a constant such pressures in equilbm.this p is due to balancing of wt of the molecule. if an excess pressure is applied then a net pressure acts on the molecule, which it transmits.
-to the best of my knowledge
Vatsal.mehtalia ( talk) 07:11, 21 January 2008 (UTC)
well here is a simple observation
consider 2 sides of a U tube, one with area A1 and other A2
A1.d1 is the displacement of one side and A2.d2 is the displacement of the other
A1.d1=A2d2 if fluid is incompressible
hence work done
F1.d1=F2.d2
hence d1/d2=F2/F1=A2/A1
Hence:
F1/A1 = F2/A2 —Preceding
unsigned comment added by
Alokdube (
talk •
contribs)
11:06, 25 November 2009 (UTC)
However the above has no bearing to how the liquid has the same level or why the pressure should be same inside the liquid —Preceding
unsigned comment added by
Alokdube (
talk •
contribs)
11:08, 25 November 2009 (UTC)
My thanks to the author that wrote the description of pressure in this section, where it is written that if you add some new surface within some gas container, that the pressure is going to still be the same no matter where the new surface is placed (well, also assuming that you make adjustments with the original surfaces that you are going to be comparing to). Now, what I would like to know is what the actual " force (mass-acceleration) per unit area" actually is. Clearly, pressure is going to be defined as the gas molecules that are bumping into the surface making up its container, but what does that mean? Does that mean that the size of the molecule is making some sort of "contact plane" with the side of the container? What about when the container of the gas is spherical, there'd be finite size to the molecules but not to the container (assume it is perfectly spherical, so there's no definite points of contacts, only intervals, right?), what then? That "contact plane" is what I am mostly asking about. The origin of this all is my own questioning on what is pressure, to better understand Avogadro's law. I know that these are approximations and that one could simply deal with the given variables, but I am more interested in the complexities that arise in the bigger questions. Thank you, -- kanzure 17:52, 22 March 2007 (UTC)
Also, while I am at it, what would be the pressure of some very large, singular gas molecule that fills up, say, my one
liter spherical container, or box container if the spherical calculations turn out to be more trouble than they are worth? Again, thank you. --
kanzure
17:52, 22 March 2007 (UTC)
As a Theoretican... In relativity, pressure is not a scalar as stated in the article, but an element of a covariant tensor; it varies under coordinate transformations. See the Wikipedia article on the Stress-Energy tensor. I believe it is also true where pressure is an element of the Newtonian stress tensor.
Also, where we may not be so interested in relativity the argument for scalar value is incomplete and/or incorrect. Is it a scalar or a pseudo scalar? That is: How does its sign behave under C,P,T and combined symmetry transformations?
If I were given its dimension [mass/(time^2.distance)] or even basic units of [k/(s^2,m)], I would have found this article useful.
-- Decraig1 ( talk) 21:06, 5 August 2013 (UTC)
"This tensor may be expressed as the sum of the viscous stress tensor minus the hydrostatic pressure. The negative of the stress tensor is sometimes called the pressure tensor, but in the following, the term "pressure" will refer only to the scalar pressure.[citation needed]"
The first sentence reads awkward, the "sum of" suggest two terms follow but instead of a second term I read a minus operation. The second sentence up to the comma is/reads incorrect afaik. If "stress tensor" means total stress (hydrostatic + dynamic) then it seems incorrect. If it means -pI or something else then it could use some rewriting.
I don't have the experience to fix what is wrong with this page... The math functions are all messed up.
(Trying to settle a small revert war between me and another user.)
People from Commonwealth countries often refer to U.S. units as "Imperial Units". That is not correct. U.S. units are a simplification of the customary systems that the colonies inherited from England. These were not Imperial units, which were not defined until 1824, long after the U.S. became independent.
Some units are the same in both systems, including weight. Others have the same name but are not the same. An Imperial gallon, for example, is larger than a U.S. gallon.
Thus it does not make sense to refer to any measure based on the customary definition of the pound as "US" (the Imperial system uses it too) or "Imperial" (the unit is used in at least one other system). -- Isaac R ( talk) 23:03, 26 July 2008 (UTC)
I find these tables that compare various units interesting but
1) they are also confusing to the novice because they do not explicitly explain how to convert 2) they are necessarily limited to about a half dozen columns, that is, only relations among a few units can be shown.
Instead I suggest basing a new table on the standard international unit with all the other units listed with their explicit conversion factors to and from the SIU. Joseph Grcar ( talk) 16:18, 29 July 2008 (UTC)
Given that a real gas has an unknown fundamental thermodynamic relation, its equation of state must necessarily also be unknown, therefore I will remove the reference to an equation for a real gas. LeBofSportif ( talk) 22:39, 29 July 2008 (UTC)
Shouldn't a statistical definition to be included on this page be proper? —Preceding unsigned comment added by Mppf ( talk • contribs) 01:07, 11 August 2010 (UTC)
1 Pa should equal 0.00001 Bar, not 0.0001 Bar. — Preceding unsigned comment added by 166.147.64.27 ( talk) 16:39, 11 September 2011 (UTC)
A well must be perforated at 8500 ft. The casing is full of 9.5 ppg mud. The well has 32 degree API gravity oil in the well and the fluid level is at 4400 ft. with a gas surface pressure of 820 psi and a gas gravity of .8. What is the pressure differential between the casing and tubing? How do I figure this out??
32 degree API gravity oil is = 7.22 lbs/gal the gas gravity of .8 is = 1.2894 — Preceding unsigned comment added by 12.230.15.34 ( talk) 16:44, 14 November 2012 (UTC)
I expected to find a mention of Pascal's vases in this article, but there isn't one; nor do they seem to have an article of their own. Are Pascal's vases just considered to be a historical curiosity and not important any more? Dezaxa ( talk) 13:52, 4 January 2013 (UTC)
I would really contest the phrase "Negative pressure must exist at the top of any tree taller than 10 m". It doesn't sound scientific at all... You imagine a 50 meters tall ladder with minions that pass a bucket of water from hand to hand to the top... There is no negative pressure on the ladder, even if the minions are soaked wet and touch each other... In fact, the whole ascent of sap article (linked at the negative pressure section) is kinda gibberish...(if it would be true, then the sap will raise to the top of a dead tree too, because there is no structural difference between green wood and dead wood, they have the same capillarity, etc). — Preceding unsigned comment added by 223.27.210.130 ( talk) 10:53, 25 October 2013 (UTC)
The introductory section of this article contains the following sentence:
A pressure of 1 Pa is small; it approximately equals the pressure exerted by a dollar bill resting flat on a table.
This sentence is parochial: it would be an unhelpful example to anyone not familiar with US currency. Such an example is unhelpful. I suggest removing it unless a replacement can be found which is less culturally specific.
Chrislaing ( talk) 21:20, 9 December 2013 (UTC)
Hello Trackteur, I think that in lists and comparisons of pressure units, each unit should wikilink to the article about the unit, even though it has been wikilinked already. I think that at such places the wikilink usefulness outweighs the repeated link ugliness. Petr Matas 20:11, 17 August 2014 (UTC)
I think that DHeyward's statement about energy equation is incorrect. Unlike pressure, the gravitational potential energy is not a function of position of measurement, but rather of position of the liquid body's center of gravity (and depends also on the choice of the zero height level), because it is an integral quantity. Therefore, the statement "energy is constant throughout the vessel" is a nonsense. Unless this is fixed somehow (I doubt that it is possible), I think that the paragraph should be removed. Petr Matas 06:46, 7 November 2014 (UTC)
Thus an increase in the speed of the fluid – implying an increase in both its dynamic pressure and kinetic energy – occurs with a simultaneous decrease in (the sum of) its static pressure, potential energy and internal energy. If the fluid is flowing out of a reservoir, the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit volume (the sum of pressure and gravitational potential ρ g h) is the same everywhere.[1] It's the reason there is a static pressure drop when fluid changes from static to flowing in a horizontal pipe: pressure energy is converted to kinetic energy. I'll add the citation. -- DHeyward ( talk) 15:30, 7 November 2014 (UTC)
References
I was surprised that I can't seem to find an article or section anywhere on Wikipedia where it actually discusses compression heating and decompression cooling, except for a brief bit in Compression ignition engine. Probably there is some discussion in pages on HVAC and refrigeration as well, but what I'm looking for is a technical page I can link to so people can read about why fluids (i.e. air) heat up when pressurized (well, compressed, anyway). I've looked on the page on Compressed air, and it says nothing. I believe it mentioned it on the page on Bleed air as well (it's been a while), but the point is, that none of these are really relevant to link to if I wanted to link to a page explaining why air heats as it's compressed. For example, I was on the page on Gas compressor(or maybe it was the page on Rotary screw compressors), and it mentions the elements of the system dedicated to "cooling the compressed air", but it doesn't say anything else. I thought it might be useful to link to a page explaining why the air would NEED cooling, but I can't find anything, unless I wanted to link to the page on diesel engines and let them read between the lines. Which doesn't seem very encyclopedic, somehow. .45Colt 07:16, 19 August 2015 (UTC)
Pressure on ears is the same as pressure on other parts of the body at the same depth. Why specify ears? • • • Peter (Southwood) (talk): 05:59, 5 August 2016 (UTC)
Is there a variant of pressure that is used for force over 3-dimensional volume?? If not, please explain why. Georgia guy ( talk) 14:59, 1 May 2017 (UTC)
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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
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)
The usage on the page is inconsistent. Then shouldn't it be pV=nRT? I've always seen P used for pressure in the ideal gas law. I know that P is phosphorus, but in every chem book I've ever seen, it seems that P is used for pressure, too. I think the page needs to be changed to "(symbol: 'p' or 'P')" in order to be correct. Any comments about this? Sushilover2000 ( talk) 15:13, 17 November 2008 (UTC)
I'm in mechanical engineering specializing in fluids and I can say that I've seen no adherence to any convention between sources. It's entirely context-driven, ie left to the discretion of the author to not confuse the reader. To say that big P is reserved for power is simply wrong as I can pull a dozen sources on fluid mechanics in five minutes that directly contradict that. I honestly don't know why so much fuss is being made over whether the p is capitalized or not anyway. The p represents pressure when the author is talking about pressure, regardless of capitalization. Though I do think the p sometimes P bit is wordy and unnecessary since stating the letter p is use for pressure seems sufficient. In my experience there is very little convention for capitalization on many variables. I've seen i and I for current, p and P for power, l and L for length. Iron_Engineer ( talk) 18:08, 1 July 2009 (UTC)
I added a reference to the IUPAC standard (lower-case p), and moved the footnote into the body of the text. I first came to this article to figure out if pressure should be p or P, so I expect some others will be looking for that information. The lack of consensus, which was conveyed by the footnote, is worth including in the body of the article (I think). Christopher King ( talk) 13:30, 20 December 2015 (UTC)
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.
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
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 i still dont get it
There is room for improvement here. I hope to get to making edits soon, but will put some thoughts here and try for some feedback first. Maybe one of you is better at this stuff than I am anyway. Here are some areas I hope to address:
Seanmichaelmcintyre ( talk) 19:05, 25 April 2013 (UTC)
The section about pressure as potential energy doesn't hold true for incompressible liquids. Take a hydraulic cylinder. YOu can increase the pressure but without a change in volume. Therefore no work in there will be no work out. — Preceding unsigned comment added by 68.47.28.48 ( talk) 03:32, 18 July 2020 (UTC)
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)
Somebody has sabotaged the formula. 68.149.173.141 ( talk) 02:24, 14 January 2010 (UTC)
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)
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)
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)
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)
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)
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)
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)
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)
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)
Hey what about 'ksca'? The unit 'kilogram per square centimeter absolute' is used sometimes too. I had a hell lot of trouble finding it's expansion as its more usual form kg/cm2 is so common and I could not immediately make the connection (though I was trying to see if anything fits in as with 'psi' and 'pounds per square inch', so very dumb of me!). Elncid ( talk) 11:21, 16 January 2008 (UTC)
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)
asap .. The only thing to manage is to lie on the bed such that the pressure on all the nails is equal. In each and every surface there are some irregularities that interlock , thus a type of surface is formed by the nails.-- 115.240.129.38 ( talk) 16:21, 6 September 2009 (UTC)
That 10^-6 should be 10^-4.
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 ?
mga tae kc ung pressure n nagsamasama upang makbuo ng isang boung malikng pressure —Preceding unsigned comment added by 203.111.234.59 ( talk) 09:50, 16 January 2009 (UTC)
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):
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)
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)
So what's wrong with what the article currently says, which is "gage (sometimes spelled gauge)"? linas 05:13, 11 December 2006 (UTC)
Why is this (important) question in metrology the second section of the article? The definition of pressure is the same, whether its is measuered ga(u)ge or absolute. Gauge pressure and gage pressure should not redirect here. Physchim62 (talk) 13:22, 11 December 2006 (UTC)
Rather than Nick Y's ill-informed rampant speculation about some "error" caused by "spell-checkers" in the last "10-15 years", let's just look at what the experts in some reliable sources have to say about that. Here's Webster's Third New International Dictionary, Unabridges, 1961:
Note that for definition 3, the use of this variant is not limited to a particular definition of the word. Nor is it limited to a particular part of speech. This variant is one used for any of the various meanings of gauge, whether used as a noun, as a verb, as an adjctive, or whatever.
And, by the way, for the math-challenged among you, 1961 is more than "10-15 years ago." Gene Nygaard 22:19, 12 December 2006 (UTC)
Webster's Third, 1961:
Note that there is no entry for "gage pressure". Gene Nygaard 22:43, 12 December 2006 (UTC)
All that really matters is the etymology. Webster's Third, 1961:
You might want to go check out Middle English, to see if this likely results from the "use of spell-checkers in the past 10-15 years"! It turned into Early Modern English over 600 years ago. What do you have to say now, Nick Y? Gene Nygaard 22:49, 12 December 2006 (UTC)
This section intentionally blank, and likely to remain so.
I think you need to chill a bit, ...Dude. As I stated when I entered this thread I am an impartial editor. I think you might infer from that that I am not claiming to be an expert. My qualifications or age aren't particularly relevant except being a level headed editor. My conclusion was that we should use gauge first and reference gage secondarily based on the British evidence provided by Greg L. I think we need to hash out the current and historical usage of both words. This includes scientific and engineering usage and not just dictionary definition. The Webster's 3rd 1961 definition seems to validate your point very well. Thank you for bringing this to our collective attention. With the additional references from the past it seems clear that "gauge" and "gage" have been interchangeable in this usage in the US in some people's eyes for quite a while if not forever. It remains true however that gage is very heavily used in the US scientific and engineering fields and the use of gauge is frowned upon by some. It is also true that the use of gage appears to be declining. I still believe that this phenomenon is due to my spell checker hypothesis despite whether gauge is an acceptable interchangeable spelling. It simply looks more familiar to most people. But all of that is irrelevant. For the purpose of this article I would say that "gauge (also gage)" or perhaps "gauge (also gage in US English)" will suffice. I think we are done here? Peace-- Nick Y. 18:46, 13 December 2006 (UTC)
Feel free to add other references to those subsections if you like, Nick or anybody else. Just stop the wild speculation that has generally proved to be false. Here, for what it is worth, are some results of Google searches. Gene Nygaard 16:09, 14 December 2006 (UTC)
hits | |
---|---|
"pressure gauge" -Wikipedia | 1,240,000 |
"pressure gage" -Wikipedia | 195,200 |
"gauge pressure" -Wikipedia | 383,000 |
"gage pressure" -Wikipedia | 83,300 |
gauge psig | 480,000 |
gage psig | 139,000 |
gauge kPa OR MPa | 1,000,000 |
gage kPa OR MPa | 337,000 |
site:xxx | |||||||
---|---|---|---|---|---|---|---|
.org | .edu | .mil | .uk | .ca | .au | nist.gov | |
"pressure gauge" | 304,000 | 1,250,000 | 9,390 | 114,000 | 32,100 | 38,500 | 163 |
"pressure gage" | 27,600 | 198,000 | 570 | 1,080 | 1,150 | 337 | 58 |
"gauge pressure" | 59,900 | 391,000 | 205 | 902 | 686 | 692 | 67 |
"gage pressure" | 12,200 | 84,200 | 231 | 435 | 289 | 81 | 38 |
Please allow me to say that I am by no means an expert in this field. Rather just a student who has studied gauge pressure in General Physics. I have nothing but for respect for anyone entrenched in this field but I just wanted to offer an opinon from the side of what's being taught in schools. "University Physics" by Young and Freedman, volumes I and II refer to the spelling of gauge pressure and not gage pressure. Also from what I've understood it's called gauge pressure because it's measure on a gauge excluding atmospheric pressure, hence that's where the spelling comes from. Further I believe the more common spelling of gauge has been established by
Gene Nygaard that the world overwhelmingly uses the spelling gauge pressure. As such I vote to support gauge pressure--
Robert Stone, Jr.
03:47, 5 January 2007 (UTC)
It seems "gauge pressure" is the consensus here --- Safemariner 04:57, 8 January 2007 (UTC)
[sigh...] Where to begin? I am a humble copy editor who came across this article because it was tagged with {{copyedit}}. The issue was an inconsistency in the spelling of the word gauge (also spelled gage)—or is it gage (also spelled gauge)? Words cannot express my reluctance to revisit this debate, which I thought was resolved in January 2007. Here is what I will do:
I hope this will address the copy edit issue, and respect the consensus of the editors involved. Cheers. Braincricket ( talk) 09:22, 4 January 2012 (UTC)
To unnecessarily (and probably unwisely) re-visit a bitter (and long...I ran out of popcorn!) debate, I just felt I had to add my own personal observation that it always strikes me as foolish when people act as if a change in a words pronunciation or spelling was desecrating thousands of years of history written in stone, when language has changed constantly throughout history (and will continue to do so), and when "official spellings" as such were non-existent or unknown up until quite recently. At some point, people decided they would sit down and freeze language into stone, which I think is a futile attempt doomed to failure, and whenever certain people see other people using the "official" language "incorrectly", they form a mob and break out the torches. It's even worse in cases like this where they disagree on what the official spelling even is. Granted, in fields of scientific endeavor, some terms must be made constant and uniform, but in this particular case, does it really matter that much whether it's spelled "gage" or "gauge"? You might loose a little precision, but the while thing isn't worth starting a jihad over, especially since it's unlikely that proponents of one variant will ever change the way people in another country spell the word. I think it's wiser to simply educate people if they see "gauge pressure" or "gage pressure", they may well mean the same thing, and it's up to them to be aware of this and use common sense. Most people dealing with this sort of thing ought to be intelligent enough to muddle through a small difference in spelling if they know that it could mean either thing. Personally, I prefer "gauge", for the simple reason that I consider "gage" to be ugly (a dumb reason, yes). That's also why I use "grey" instead of "gray", even though it's "incorrect" to do so. Unless you live in the UK, anyway.
One question though, I'd genuinely like to know...one sentence in the above debate seems to be saying that "gage" is pronounced differently than "gauge". Is this true? He says that
"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."
So "gage" is pronounced "jahy-juh" then? That's certainly a education for me. If it's not true, I fail to see what the relevance is...is the auto store man supposed to spell it out for him? How are two words spelled differently and pronounced the same the same thing as a word that was simply misread and entered public consciousness in a way it wasn't originally intended to do. A "gigawatt" is a "gigawatt", regardless of how you pronounce it, while the whole point of the complaining side of this debate is that that "gauge" and "gage" have two different meanings, in spite of being pronounced the same. I fail to see any real parallel there.
As a last note, for what it's worth, I was taught at some place or other that "gage" is simply an American simplification of the older British term "gauge", but both are considered correct spellings in the US (of course, in that context it was referring to "gauges" such as instruments). I believe I looked it up, because the first time I saw "gage" written out, I assumed it was a spelling error, because I'd never seen it spelled that way before. .45Colt 07:48, 19 August 2015 (UTC)
I deleted the Biology part since it was just vandalism by someone who was trying to be funny. Ranmamaru 06:29, 11 January 2007 (UTC)
ok so volume of a liquid has to be conserved (given it is incompressible, non viscous blah blah) but why should the force per unit area be conserved and be the same in all directions? Basically if I just model everything as volume conservation and simply try and say that the liquid "en mass" will try to attain a level of minimal potential energy, I still end up with the same results. However to make the assumption that dF/dA is conserved seems off beat to me. —The preceding unsigned comment was added by 220.227.207.194 ( talk) 09:28, 5 March 2007 (UTC).
ans. analytically u can consider pressure on a liquid molecule as a contact push due to vertical( upward )layer of molecules constantly acting on it. hence it is a summation a constant such pressures in equilbm.this p is due to balancing of wt of the molecule. if an excess pressure is applied then a net pressure acts on the molecule, which it transmits.
-to the best of my knowledge
Vatsal.mehtalia ( talk) 07:11, 21 January 2008 (UTC)
well here is a simple observation
consider 2 sides of a U tube, one with area A1 and other A2
A1.d1 is the displacement of one side and A2.d2 is the displacement of the other
A1.d1=A2d2 if fluid is incompressible
hence work done
F1.d1=F2.d2
hence d1/d2=F2/F1=A2/A1
Hence:
F1/A1 = F2/A2 —Preceding
unsigned comment added by
Alokdube (
talk •
contribs)
11:06, 25 November 2009 (UTC)
However the above has no bearing to how the liquid has the same level or why the pressure should be same inside the liquid —Preceding
unsigned comment added by
Alokdube (
talk •
contribs)
11:08, 25 November 2009 (UTC)
My thanks to the author that wrote the description of pressure in this section, where it is written that if you add some new surface within some gas container, that the pressure is going to still be the same no matter where the new surface is placed (well, also assuming that you make adjustments with the original surfaces that you are going to be comparing to). Now, what I would like to know is what the actual " force (mass-acceleration) per unit area" actually is. Clearly, pressure is going to be defined as the gas molecules that are bumping into the surface making up its container, but what does that mean? Does that mean that the size of the molecule is making some sort of "contact plane" with the side of the container? What about when the container of the gas is spherical, there'd be finite size to the molecules but not to the container (assume it is perfectly spherical, so there's no definite points of contacts, only intervals, right?), what then? That "contact plane" is what I am mostly asking about. The origin of this all is my own questioning on what is pressure, to better understand Avogadro's law. I know that these are approximations and that one could simply deal with the given variables, but I am more interested in the complexities that arise in the bigger questions. Thank you, -- kanzure 17:52, 22 March 2007 (UTC)
Also, while I am at it, what would be the pressure of some very large, singular gas molecule that fills up, say, my one
liter spherical container, or box container if the spherical calculations turn out to be more trouble than they are worth? Again, thank you. --
kanzure
17:52, 22 March 2007 (UTC)
As a Theoretican... In relativity, pressure is not a scalar as stated in the article, but an element of a covariant tensor; it varies under coordinate transformations. See the Wikipedia article on the Stress-Energy tensor. I believe it is also true where pressure is an element of the Newtonian stress tensor.
Also, where we may not be so interested in relativity the argument for scalar value is incomplete and/or incorrect. Is it a scalar or a pseudo scalar? That is: How does its sign behave under C,P,T and combined symmetry transformations?
If I were given its dimension [mass/(time^2.distance)] or even basic units of [k/(s^2,m)], I would have found this article useful.
-- Decraig1 ( talk) 21:06, 5 August 2013 (UTC)
"This tensor may be expressed as the sum of the viscous stress tensor minus the hydrostatic pressure. The negative of the stress tensor is sometimes called the pressure tensor, but in the following, the term "pressure" will refer only to the scalar pressure.[citation needed]"
The first sentence reads awkward, the "sum of" suggest two terms follow but instead of a second term I read a minus operation. The second sentence up to the comma is/reads incorrect afaik. If "stress tensor" means total stress (hydrostatic + dynamic) then it seems incorrect. If it means -pI or something else then it could use some rewriting.
I don't have the experience to fix what is wrong with this page... The math functions are all messed up.
(Trying to settle a small revert war between me and another user.)
People from Commonwealth countries often refer to U.S. units as "Imperial Units". That is not correct. U.S. units are a simplification of the customary systems that the colonies inherited from England. These were not Imperial units, which were not defined until 1824, long after the U.S. became independent.
Some units are the same in both systems, including weight. Others have the same name but are not the same. An Imperial gallon, for example, is larger than a U.S. gallon.
Thus it does not make sense to refer to any measure based on the customary definition of the pound as "US" (the Imperial system uses it too) or "Imperial" (the unit is used in at least one other system). -- Isaac R ( talk) 23:03, 26 July 2008 (UTC)
I find these tables that compare various units interesting but
1) they are also confusing to the novice because they do not explicitly explain how to convert 2) they are necessarily limited to about a half dozen columns, that is, only relations among a few units can be shown.
Instead I suggest basing a new table on the standard international unit with all the other units listed with their explicit conversion factors to and from the SIU. Joseph Grcar ( talk) 16:18, 29 July 2008 (UTC)
Given that a real gas has an unknown fundamental thermodynamic relation, its equation of state must necessarily also be unknown, therefore I will remove the reference to an equation for a real gas. LeBofSportif ( talk) 22:39, 29 July 2008 (UTC)
Shouldn't a statistical definition to be included on this page be proper? —Preceding unsigned comment added by Mppf ( talk • contribs) 01:07, 11 August 2010 (UTC)
1 Pa should equal 0.00001 Bar, not 0.0001 Bar. — Preceding unsigned comment added by 166.147.64.27 ( talk) 16:39, 11 September 2011 (UTC)
A well must be perforated at 8500 ft. The casing is full of 9.5 ppg mud. The well has 32 degree API gravity oil in the well and the fluid level is at 4400 ft. with a gas surface pressure of 820 psi and a gas gravity of .8. What is the pressure differential between the casing and tubing? How do I figure this out??
32 degree API gravity oil is = 7.22 lbs/gal the gas gravity of .8 is = 1.2894 — Preceding unsigned comment added by 12.230.15.34 ( talk) 16:44, 14 November 2012 (UTC)
I expected to find a mention of Pascal's vases in this article, but there isn't one; nor do they seem to have an article of their own. Are Pascal's vases just considered to be a historical curiosity and not important any more? Dezaxa ( talk) 13:52, 4 January 2013 (UTC)
I would really contest the phrase "Negative pressure must exist at the top of any tree taller than 10 m". It doesn't sound scientific at all... You imagine a 50 meters tall ladder with minions that pass a bucket of water from hand to hand to the top... There is no negative pressure on the ladder, even if the minions are soaked wet and touch each other... In fact, the whole ascent of sap article (linked at the negative pressure section) is kinda gibberish...(if it would be true, then the sap will raise to the top of a dead tree too, because there is no structural difference between green wood and dead wood, they have the same capillarity, etc). — Preceding unsigned comment added by 223.27.210.130 ( talk) 10:53, 25 October 2013 (UTC)
The introductory section of this article contains the following sentence:
A pressure of 1 Pa is small; it approximately equals the pressure exerted by a dollar bill resting flat on a table.
This sentence is parochial: it would be an unhelpful example to anyone not familiar with US currency. Such an example is unhelpful. I suggest removing it unless a replacement can be found which is less culturally specific.
Chrislaing ( talk) 21:20, 9 December 2013 (UTC)
Hello Trackteur, I think that in lists and comparisons of pressure units, each unit should wikilink to the article about the unit, even though it has been wikilinked already. I think that at such places the wikilink usefulness outweighs the repeated link ugliness. Petr Matas 20:11, 17 August 2014 (UTC)
I think that DHeyward's statement about energy equation is incorrect. Unlike pressure, the gravitational potential energy is not a function of position of measurement, but rather of position of the liquid body's center of gravity (and depends also on the choice of the zero height level), because it is an integral quantity. Therefore, the statement "energy is constant throughout the vessel" is a nonsense. Unless this is fixed somehow (I doubt that it is possible), I think that the paragraph should be removed. Petr Matas 06:46, 7 November 2014 (UTC)
Thus an increase in the speed of the fluid – implying an increase in both its dynamic pressure and kinetic energy – occurs with a simultaneous decrease in (the sum of) its static pressure, potential energy and internal energy. If the fluid is flowing out of a reservoir, the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit volume (the sum of pressure and gravitational potential ρ g h) is the same everywhere.[1] It's the reason there is a static pressure drop when fluid changes from static to flowing in a horizontal pipe: pressure energy is converted to kinetic energy. I'll add the citation. -- DHeyward ( talk) 15:30, 7 November 2014 (UTC)
References
I was surprised that I can't seem to find an article or section anywhere on Wikipedia where it actually discusses compression heating and decompression cooling, except for a brief bit in Compression ignition engine. Probably there is some discussion in pages on HVAC and refrigeration as well, but what I'm looking for is a technical page I can link to so people can read about why fluids (i.e. air) heat up when pressurized (well, compressed, anyway). I've looked on the page on Compressed air, and it says nothing. I believe it mentioned it on the page on Bleed air as well (it's been a while), but the point is, that none of these are really relevant to link to if I wanted to link to a page explaining why air heats as it's compressed. For example, I was on the page on Gas compressor(or maybe it was the page on Rotary screw compressors), and it mentions the elements of the system dedicated to "cooling the compressed air", but it doesn't say anything else. I thought it might be useful to link to a page explaining why the air would NEED cooling, but I can't find anything, unless I wanted to link to the page on diesel engines and let them read between the lines. Which doesn't seem very encyclopedic, somehow. .45Colt 07:16, 19 August 2015 (UTC)
Pressure on ears is the same as pressure on other parts of the body at the same depth. Why specify ears? • • • Peter (Southwood) (talk): 05:59, 5 August 2016 (UTC)
Is there a variant of pressure that is used for force over 3-dimensional volume?? If not, please explain why. Georgia guy ( talk) 14:59, 1 May 2017 (UTC)
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