Talk:Standard atmosphere (unit)

Comments by IP

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1atm = 1.01325*10^5 ?!?!

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—Preceding unsigned comment added by 129.125.180.7 (talk) 19:20, 23 August 2008 (UTC)

<nowiki>Insert non-formatted text here<nowiki>Insert non-formatted text here<nowiki>Insert non-formatted textt5 tttttghere</nowiki></nowiki></nowiki>plz tell me about vacuum rtgggdistillation in detail n vacuum distillation tower for napthenic based crude oils --203.135.37.182 11:47, 28 May 2006 (UTC)nauman

hello i just want to know what is something that is less than 1 atm...203.87.190.46 09:06, 31 December 2006 (UTC)

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Error in definition

Standard Atmosphere is not a unit of pressure! Standard Atmosphere refers to pression of 101 325 Pa. See http://goldbook.iupac.org/S05906.html

Contributions from (user:Mago® - Wiki-pt)

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Note the bit on that page where it says "used as unit of pressure with the symbol atm..." --Calair 17:43, 30 April 2007 (UTC)

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"Standard atmosphere (symbol: atm) is a unit of pressure". Why not? "as unit of pressure with the symbol" . Contributions from (user:Mago® - Wiki-pt) —The preceding unsigned comment was added by 200.161.58.39 (talk) 23:19, 30 April 2007 (UTC).

I'm really not seeing a meaningful difference between "is a unit of pressure" and "is used as a unit of pressure". --Calair 02:51, 1 May 2007 (UTC)

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Hi Calair. The problem is:

• Article Standard atmosphere:

"Standard atmosphere (symbol: atm) is a unit of pressure..."

Traduction: Standard atmosphere = unit

Comments: No. Unit = atm, Pa, ºC, ºF, K. The value 101 325 Pa is a pressure used as unit of pressure.

• IUPAC:

Pressure defined as 101 325 Pa and used as unit of pressure with the symbol atm.

Traduction: Standad atmosphere = Pressure = 101 325 Pa.

Sorry for my bad English. ;(

Hugs from Brazil (Abraços brasileiros)

Mago® - Wiki-pt:

<http://pt.wikipedia.org/wiki/Usu%C3%A1rio:Lemarlou>

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Hi Calair.

Standard Atmosphere = 101 325 Pa = Normal.

The normal term means a value at a pressure of 101 325 Pa too.

See:

http://goldbook.iupac.org/N04211.html

Add this information for me in Wiki-en. ;) Thanks

Please... do you speak portuguese? YES ( ) No ( ) ?

)

Greetings from Mago® (Wiki-Pt) <http://pt.wikipedia.org/wiki/Usu%C3%A1rio:Lemarlou>

I don't speak Portuguese, so I don't know if there's a translation problem here, but 'atm' and 'standard atmosphere' are simply different ways of referring to the same unit, in the same way that 'Pa' is an abbreviated version of 'Pascal'. Maybe you're getting confused with SI units? A standard atmosphere isn't a SI unit, but it most certainly is a unit of pressure. --Calair 14:29, 1 May 2007 (UTC)

Atmosphere as a Unit

It is important to realise that it is an obsolete unit, but still in colloquial use (and on lots of older pressure gauges). For general engineering use there is usually little practical difference between 14 atm and 14 bar, and common gauges are only accurate to 2% FSD (on the day you buy them). Of course for precision work there are instruments and situations for which it matters. Anyone doing such work today would use the bar or pascal. Chemical Engineer (talk) 21:09, 5 September 2008 (UTC)

Yes, an obsolete unit also because the energy of the atmosphere is growing so is the gas pressure in there. 80.186.177.245 (talk) 07:15, 7 July 2009 (UTC)

Atmosphere as a unit used by divers

I propose an edit regarding the note of use of atmospheres by divers. There is widespread ignorance of units, but divers use atm correctly for partial pressures of gases such as oxygen - it is by no means obsolete.

For example, the PO2 of oxygen is approx 0.209, and when calibrating this on a rebreather it is important the number is correct - it is adjusted for atmospheric pressure and sometimes, for humidity. As PO2 sensors are calibrated at sea level, atm is the appropriate unit of measure, not the bar. Given this, the entry should read: "Use of atm by divers:

a. Units of atm are used by divers, particularly when calibrating partial pressures of oxygen. Rebreathers are normally calibrated or checked in air at sea level, so the atmosphere and not the bar is the appropriate unit.

b. Older divers in the UK continue to use ata as an obsolete unit of pressure that is applied loosely to be bar or atm - it is defined by the water pressure at 33 ft. "

Any comments / better suggestion / counterproposal? —Preceding unsigned comment added by 61508Assoc (talk • contribs) 14:02, 29 December 2009 (UTC)

IUPAC, atm and standard pressure

There's been some confusion in this article lately between (a) the value of the unit of measurement called standard atmosphere and abbreviated as atm and (b) the value of a standard or reference pressure. As of 24 March 2015 the article had been edited to give a value of 100 kPa for the unit of measurement, but that is the value of IUPAC's recommended standard pressure, not of the unit. As the article stated,[1],

However, in 1982, the International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the physical properties of substances, “the standard pressure” should be defined as precisely 100 kPa (1 bar).

and as the IUPAC Gold Book says on the Gold Book page cited

standard pressure: Chosen value of pressure denoted by p^⦵ or p°. In 1982 IUPAC recommended the value 10⁵ Pa, but prior to 1982 the value 101325 (=1 atm) was usually used.

It's important to note that IUPAC did not redefine the unit of measurement which is the subject of this article and indeed the IUPAC Gold Book still explicitly states that 101325 Pa = 1 atm, not just in the above quote but also here:

standard atmosphere: Pressure defined as 101 325 Pa and used as unit of pressure with the symbol atm.

It's not surprising that IUPAC didn't suggest a redefinition of the unit; just consider the difficulties in gaining cross-discipline, cross-industry international agreement and the repercussions. The historic discrepancies in the value of the litre are bad enough, and they were less than 0.003%, not over 1.3%.
I'll edit this article accordingly. Anyone interested in standard or reference pressures and atmospheres will find articles at Standard conditions for temperature and pressure, U.S. Standard Atmosphere, and I suspect at many other locations such as Standard cubic foot and SCFM. NebY (talk) 10:08, 28 March 2015 (UTC)

While editing, I removed the reference[2] for the original definition being based on mean sea-level pressure at Paris; that web page's text is taken from Wikipedia and the site is WP:USERGENERATED. I've tagged the claim for citation again. NebY (talk) 11:07, 28 March 2015 (UTC)

Thanks. I've been busy, mostly elsewhere, and hoped that someone would fix the recent edits. Johnuniq (talk) 01:34, 29 March 2015 (UTC)

Hi, I made the bold edits. It's clear based on your goldbook edit (and I apologize for the circular reference, so I'm glad you posted that one!) that IUPAC intends for the new definition of an atm to be 10 kPa since 1983. 10 kPa makes everything easier, and IUPAC as mentioned above doesn't want to take a stand by defining an atm - *but clearly recommends it be 10 kPa = 1 atm*. Have you ever looked at why it was 101.325? Finally, there is NO DISTINCTION between standard pressure and 1 atm. It's in the goldbook. I'm sincerely hoping this doesn't turn into WP:OWNERSHIP like all non-progressive pages. Progress! Cpt ricard (talk) 01:40, 22 May 2015 (UTC)

The IUPAC Gold Book very clearly distinguishes, as you can see in the two quotations from it above, between reference conditions and units of measurement. For the first, it recommends a standard pressure of 100 kPa (not 10 kPa). But for the second, it makes no attempt whatsoever to redefine the unit of pressure called "standard atmosphere", symbol "atm", and it repeats the definition of it as 101.325 kPa. It does not at any point do as you wrote, "clearly recommends it be 10 kPa = 1 atm".

I'm startled to see that you have now edited Pascal (unit), so that it now reads "On Earth, standard atmospheric pressure is 100 kPa; until 1983 it was defined as 101.325 kPa." and "Standard atmospheric pressure is 100 kPa.", both in direct contradiction of the very sources cited. It was already poorly phrased, I agree, but now it's blatantly inaccurate and contrary to sources so I will try to fix it, per WP:BRD rather than your edit comment "Update to IUPAC kPa definition. Please do not revert but use talk page."

Perhaps your edit does give us one clue as to what might be confusing you. IUPAC is not interested in normalising standard atmospheric pressure. It merely wants a standard set of conditions to be used when, for example, listing the properties of substances. You probably know that the density of a gas changes with its pressure. The viscosity and the isentropic exponent, to take two variables that are significant when determining the transport properties of a gas or measuring its flow, also change with pressure, albeit not so dramatically. Such properties are listed in all manner of sources from manufacturers' factsheets to giant handbooks such as CRC or Perry's, and it's necessary for the sources to stipulate the reference conditions for which the values supplied have been determined. In the past those varied considerably; IUPAC has sought to establish a degree of consistency by recommending a reference condition of 100 kPa. That has nothing to do with the unit of measurement, the atm.

You asked about the origins of the value of 101.325 kPa. That goes back more than a hundred years, to the common value of 760 mm Hg - the pressure exerted by 760 mm of mercury at 0°C and 9.80665 m/s², the value still used for standard gravity and which (if memory serves me right) was held to be the standard gravity at latitude 45° N. (0.76 x 13595.1 x 9.80665 = 101325.) I think the value of 760 was the closest multiple of 10 that approximated to average pressure at sea-level at about 45° N, but there may be more to it than that - none of the sources I have to hand and have checked have that detail. NebY (talk) 21:16, 22 May 2015 (UTC)

References

1 bar = 14.5 psi or 14.696 psi ?

1 bar = 14.5 psi or 14.696 psi (rounded up to 14.7 psi) ? Q. Which is correct !! 86.185.153.52 (talk) 23:42, 20 March 2017 (UTC)

1 bar = 0.986923 atm = 14.5038 psi
1 atm = 1.01325 bar = 14.6959 psi

-73.61.15.12 (talk) 20:34, 3 April 2018 (UTC)

meant to be the air pressure at sea level and the EXTRA water pressure of 10 m underwater at sea.

My edit about air pressure at sea level and the EXTRA water pressure at 10 meters underwater at sea, was reverted by user:TW and listed as a good faith edit by me, with a question in the edit: How can it be both 10 m underwater and at sea level. Here's what I wrote.

I'm putting it back, this time with a source and better worded. פשוט pashute ♫ (talk) 21:39, 2 May 2018 (UTC)

And I've removed it. It does not make sense to claim that one atmosphere was both sea level air pressure and the pressure at a 10m depth of water. The pressure at 10m underwater may coincidentally be about one atmosphere, but that's not any part of the definition. Meters (talk) 22:56, 2 May 2018 (UTC)

It made perfect sense that an EXTRA pressure of a second atmosphere is felt at the depth of 10 meters. Just as it makes sense that 760 mm of mercury are actually 760 mm PLUS the air column above it at sea level. But that was my original text which you erased the first time. In the meantime I changed what I wrote.

This time I changed the words and did not speak of underwater pressure, but rather of Torricelli's original barometers depicted in drawings of the time, and built in accordance with Galileo's writings. I even gave the source to those.

I wrote: One atomsphere was originally meant to be around the mean pressure felt by the air in the earth's atmosphere at sea level on a European coast in mild weather comfortable to the humans, and was defined as the pressure exerted by 760 mm of mercury at 0 °C and standard gravity (g = 9.80665 m/s²), also supposed to be the approximate equivalent of pressure exerted by 10 m of water, following Galileo's writings in "Two New Sciences".

I then gave the source with a link. (page 14 in the English translation of that book).

Please explain why the words: "exerted by 760 mm of mercury" makes sense while "exerted by 10 m of water" does not. פשוט pashute ♫ (talk) 10:46, 3 May 2018 (UTC)

The atmosphere unit is based on the pressure at Earth's "surface" under certain conditions. Any pressure is also the same as the pressure exerted by some height of water, whether that height is 1 mm or 1 km or anything else. The fact that 1 atmosphere is the same pressure as some height of water is a statement of the obvious and is not encyclopedic information relating to the definition of the unit. Johnuniq (talk) 11:00, 3 May 2018 (UTC)