Talk:Bar (unit)

ksi?

The photo has a caption that refers to "700 bars (10 ksi) of pressure", but nowhere is a "ksi" defined. Without doing the conversions to all the different units mentioned in the article, I really don't know what ksi could refer to or be a typo for. Anyone know what's up with it? — Preceding unsigned comment added by 173.240.25.225 (talk) 17:26, 18 January 2016 (UTC) EDIT: Never mind, I Googled it. "Kilopound per square inch" - that's a weird one. I'll edit the caption to have a link or some more clarity somehow. 173.240.25.225 (talk) 17:29, 18 January 2016 (UTC)

definitions

The bar as:

• 1 bar = 100 000 pascals (Pa) = 100 kPa1

The old definition was:

• 1 bar = 1 000 000 dynes/square centimetre

But these definitions are equivalent, so it makes no sense to say one is the "old" definition. A change of units in the way the definition is worded is not a change in definition!

1 bar = 10^6 dynes/(cm)^2 = 10^6 (10^(-5)) N/(10^(-2) m)^2 = 10 N/10^(-4) m^2 = 10^5 N/m^2 = 10^5 pascals

so the 2 definitions are equivalent. 216.167.142.251

The bar however, was traditionally defined in terms of the dyne and square centimeter, not in terms of the pascal. Andros 1337 02:58, 31 October 2005 (UTC)

Merge from millibar

Bar (unit) and millibar repeat a lot of the same material. In keeping with the precedent for merging articles on multiples and submultiples of units into the article on the "base" or unprefixed unit, millibar should be merged into this article. Indefatigable 16:33, 30 December 2005 (UTC)

Conversion

Even though bars and millibars represent atmospheric pressure rather than altitude, you can get a general estimate of the altitude by applying the following conversions. Remember that this is a general estimate. Atmospheric pressures are not constant throughout the atmosphere.

Millibars to Meters:

$h={\frac {\log \left({\frac {p}{1013}}\right)}{\log(0.88)}}\times 1000$

Meters to Millibars

$p=10^{\left({\,\!{\frac {h}{1000}}\times \log 0.88}\right)}\times 1013$

h = height in meters
p = pressure in millibars

David Mitchell 22:06, 27 February 2006 (UTC)

bara, barg - really deprecated?

I don't know about in industry but these are taught and encouraged on my university course. Seems like a convenient way of specifying absolute or gauge pressure without having to write it out in words every time. —Preceding unsigned comment added by 131.111.8.104 (talk) 23:26, 20 May 2008 (UTC)

I don't think it's deprecated. In the oil and gas industry, we use bar for differential pressure, barg for pressure indication, and bara for process calculations. I vote for removal of the statement that it is deprecated. 62.200.20.13 (talk) 10:00, 6 August 2013 (UTC)

I agree. The reference to this fact in section "Absolute pressure and gauge pressure" points to BSI, which is, as far I can tell, not a global authority. I'll remove this claim, as it is explained better earlier on the page. --Tannkrem (talk) 14:42, 21 October 2014 (UTC)

Use in aeronautics

It seems that millibars are also used to express altitude in conversations between air traffic controls and aircrafts. Can anyone confirm this?

Yes, but only to set the pressure setting on their altimeters not to specify an actual height. For instance on approach an air traffic controller may instruct a pilot to fly on a course of 270 degrees at 2000ft with a QFE of 1030. The 1030 is the pressure in millibars/hectopascals at the airfield where the pilot is intending to land. If the airfield is located at say 200ft above sea level the pilots altimeter should read more or less 200ft when the wheels contact the ground.

Above a certain height all altimeters are set to a standard setting, so pilots at 10000 ft will use a pressure setting of 1013mb regardless of the local air pressure either around them or on the ground they are flying over.

See Flight level for further details ---- M100 02:53, 11 March 2007 (UTC)

Merge from Decibars

Hi, I'm Decibars and I'm new to the neighborhood... just merged in today, thought I would say hello. MDSNYDER 05:57, 4 July 2007 (UTC)

Bars in meteorology?

Meteorology and millibars is covered somewhat in the article w/ respect to hurricanes, but in the U.S. (the National Weather Service in particular) forecasters tend to use it as an altitude, too, i.e. 850 mb level, 500 mb level. Would these be straight-up conversions to a certain number of feet, or is there another way these levels are notable? —Rob (talk) 22:13, 26 November 2007 (UTC)

Hectopascals

I reverted the edit that removed the 1 hPa from the definitions section

1 mbar = 0.001 bar = 0.1 kPa = 1 hPa = 1,000 dyn/cm²

Hectopascals are very widely used in Australia and also referred to elsewhere in the article, In my view having them in the definition section doesn't detract from the article and only improves its clarity. M100 (talk) 01:07, 15 March 2008 (UTC)

feet?

One bar equal to how many feet? —Preceding unsigned comment added by 202.60.56.249 (talk) 07:45, 27 July 2009 (UTC)

Origin

There should be more on the origins. Exactly how is it that 1 millibar = 1 hectopascal - equivalency between different systems isn't usually so round. Was the bar originally defined in terms of metric units?

76.66.196.139 (talk) 06:06, 19 September 2009 (UTC)

I agree, the origin section skips a lot. I believe (but haven't looked up) that 1 bar used to be 1 atmosphere, and I suspect its origin was simply that the typical lab manometer had horizontal bars marking each increment, so N atmospheres colloquially becomes N "bars". Then it was normalized with the advent of SI to be 100 kPa, being one of the ways in which standardization just created a schism of inaccuracy between statements made on yellowed, spotted, dittoed paper vs. those on fresh, white laser-printed paper... 68.2.235.85 (talk) 04:46, 10 May 2015 (UTC)

No, it's just a fortunate historic accident that a pressure unit made by using grams, metres and an integer power of ten is so conveniently close to atmospheric pressure. The value of the bar was not changed with the introduction of SI, just expressed differently. The etymology of bar is given in the article; it has the same root as barometer. NebY (talk) 15:44, 10 May 2015 (UTC)

Capitalization

AFAIK the bar is always lowercase (not 100% sure if it would be so at the beginning of a sentence tho), so I put the relevant tag on top of the page. I've not found similar cases elsewhere so feel free to revert if you think this is not correct. Redgolpe (talk) 09:51, 3 November 2009 (UTC)

I reverted, since all SI units are also lower case, and we don't have a consensus to special-case them; normal sentence case is assumed. Dicklyon (talk) 15:35, 3 November 2009 (UTC)

Spelling

In the paragraph: In the United States, where pressures are still often expressed in pounds per square inch (symbol psi), gauge pressures are referred to as psig and absolute pressures are referred to as psia. Gauge pressure is also sometimes spelled as gage pressure.

I think that the gage pressure should be spelled gauge pressure, but I'm not sure, maybe the point of that sentence is to say that it is spelled funny in this case. I saw this in passing, so I'm pointing it out sense I don't have the confidence to edit it. I will not likely be back to checkup on this.Trescott2000 (talk) 10:02, 3 February 2011 (UTC)

Mistake in chart?

The chart shows that 1 Pa = 0.0001 Bar, but 1 Pa should equal 0.00001 Bar. — Preceding unsigned comment added by 166.147.64.27 (talk) 16:20, 11 September 2011 (UTC)

The chart shows 1 Pa = "10^-5" Bar, which is 0.00001, not 0.0001. So there's no mistake. Hatster301 (talk) 06:48, 12 September 2011 (UTC)

Definition

The correct definition of the bar (as found in dictionaries) is 1,000,000 dynes per square centimeter, since the bar is a unit that predates the SI system. 100 kPa is just an equivalent value, however, it makes no sense say it is the definition of the bar due to the SI system not existing when the bar was originally defined. ANDROS¹³³⁷_TALK 19:05, 16 May 2012 (UTC)

units

I think this article would be clearer if more attention was paid to precisely defining the area in the differnt units eg pressure is force/unit area in some measures (PSI, Pa) this is explicti, in others (bar) it is not I think this is confusing — Preceding unsigned comment added by 50.245.17.105 (talk) 16:09, 15 July 2014 (UTC)

Specify please

                    "The bar is a non-SI unit of pressure"

then if it is not an SI unit i would like to know which category it belongs to. It seems to me it´s not an U.S. Customary unit because:

                    "In the United States, where pressures are still often expressed in pounds per square inch (symbol psi),
                    gauge pressures are referred to as psig and absolute pressures are referred to as psia. Gauge pressure is 
                    also sometimes spelled as gage pressure."

could it be of the "imperial unit", "English unit", and if it belongs to the "FPS" or "CGS" or "sistema Tecnico" (technical system(rough translation) which according to my book are out of date units used in engineering. This "technical system" might have been something only used in South America but still... i don´t know if they were also used in Europe. — Preceding unsigned comment added by 190.10.144.253 (talk) 09:45, 23 April 2013 (UTC)

                    "The bar and the millibar were introduced by the British meteorologist William Napier Shaw in 1909, 
                     while he was the director of the Meteorological Office in London."

it looks like it is part of the "English units" maybe not part of the "Imperial System(Weights and Measures Act 1824)". — Preceding unsigned comment added by 190.10.144.253 (talk) 10:07, 23 April 2013 (UTC)

Deprecated?

In the main text it says that the bar is deprecated and its use discouraged. Is that so? This same article states that the IUPAC favors its use instead of the atm to define standard conditions. Plus, most technical devices, like manometers come now measured in bars (in some case in addition to psi's, or replacing them). That doesn't look like it's being deprecated. Besides, which unit can replace it when we are talking about atmospheric pressure? Gonfer (talk) 16:29, 23 April 2013 (UTC)

The text now reads "sometimes deprecated", which doesn't make much sense: either a unit is deprecated or it isn't. I've rewritten it to say "considered deprecated by some entities", which (judging from the references) seems to be the intent. Achurch (talk) 15:10, 10 November 2013 (UTC)

Someone removed "sometimes" so now it just says "deprecated". But "sometimes deprecated" is closer to reality (although I agree that it's confusing). What's really going on is that bar is deprecated for some uses by some organizations. For example, the cited NIST SP 1038 says bar is "accepted for limited use in meteorology only" and then in the next sentence says "not accepted for use in the U.S. for other applications". It is unclear whether the earlier sentence in SP 1038 is also referring to recommendations for the US. The other cited NIST report (NIST SP 811) lists bar as one of several units that "must not be introduced in fields where they are not presently used. Further, this Guide strongly discourages the continued use of these units by NIST authors except when absolutely necessary." The other citations are similar. In short, it is misleading to say that "bar is deprecated by various bodies" and I've clarified the text. Donlibes (talk) 20:51, 28 October 2016 (UTC)

• • • New Post from concerned User, chemical engineer***

Hello, Please reread the article. THe unit of measure bar has not been deprecated. What has been made obsolete is the abreviation for bar, B. As a profession engineer, I can personally atest to the obsolesence of the use of the single letter "b" to represent the bar unit of measure. Thank you, Alex R., Edison NJ — Preceding unsigned comment added by 192.31.106.36 (talk) 16:57, 12 February 2014 (UTC)

Confusing the units bar and atm

This article does nothing at all to explain why there is a variability of 1 bar = somewhere between 14.5 PSI and 14.7 PSI.

It sounds like the bar and Pascal are a contrived measure that was supposed to equal atmospheric air pressure at sea level, but the original creator(s) slightly screwed up somewhere in their definition or measurement apparatus, and by the time the mistake was discovered, nothing could be done to correct it because other people were already relying on the "wrong" measure.

This apparently makes it not really all that different from Fahrenheit, which is also a contrived measure that set 0F and 100F at unusual definitions, and which later turned out to be wrong and then could not be corrected. I believe 100F for example was supposed to be human body temperature, but for some reason this was wrong and so we have it at "98.6F" now, off by 1.4 degrees, and uncorrectable after other people started relying on the "wrong" measurement scale.

-- DMahalko (talk) 03:41, 14 July 2016 (UTC)

You are misinformed. There is no "variability of 1 bar"; bar and atm are two different units. 1 bar is 100 kPa ( ~14.5 psi), and 1 atm = 101.325 kPa ( ~14.7 psi). This article is not about the atm unit. Ceinturion (talk) 07:50, 14 July 2016 (UTC)

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Bjerknes coined the units bar and millibar, not Napier Shaw

The current version of the article says "The bar and the millibar were introduced by the British meteorologist William Napier Shaw in 1909". That is incorrect. In 1918 Marvin, in this article about the units of absolute pressure (also published in the Quarterly Journal of the Royal Meteorological Society), stated that British Meteorological Office had used millibars in recording upper-air observations since 1907. Marvin quotes Bjerknes that he coined the unit name bar and that he employed it for the first time in a paper published in 1906*:

Meteorologists have long had occasion to express atmospheric pressures in absolute terms, but it remained reserved for Bjerknes to recognize the peculiar convenience in hydrodynamics and atmospherics of the megadyne per square centimeter as a unit of pressure, and through his pupil , J W Sandström, to introduce it - without assigning it a special name at the time - in his epochal investigations into the hydrodynamics of the sea and the atmosphere.

It soon became desirable to avoid the circumlocution of calling the unit "one million dynes per square centimeter", and Bjerknes proposed to call it the "bar" = 1 megadyne per square centimeter, with its subdivisions of decibar, centibar, millibar, etc., in accordance with the method of numeration of the C. G. S. system. Prof. Bjerknes' own account of the origin of this unit, the "bar", follows.

When fourteen years ago I began to occupy myself with problems concerning the dynamics of the atmosphere and the sea, I encountered many difficulties of terminology. Cumbrous expressions such as "Pressure at that height where gravity potential is x.10⁵ C. G. S.- units", or "gravity-potential at that height where pressure is y.10³ C. G. S.-units", as well as the corresponding expressions concerning dynamic conditions at different depths in the sea, recurred again and again, often on the same page. I therefore coined the terms ' bar,' ' decibar,' 'centibar,' and 'millibar' as names for the units of pressure; 'dynamic height,' 'dynamic depth' as synonyms for gravity-potential, and finally 'dynamic metre,' 'dynamic decimetre,' etc., for the units of this quantity. In place, then, of the cumbrous expressions which prevailed formerly, we now have "Pressure at the height of x dynamic metres", "Dynamic height of the pressure y mbar" with respect to the atmosphere, and with respect to the sea "Pressure at the depth of x dynamic metres", "dynamic depth of the pressure y dbar".

'I employed these expressions for the first time in a paper published in 1906, and expected that criticism would be directed against them, as the use of new terms usually provokes opposition ; but they passed without comment, and consequently a discussion which might have proved fruitful did not arise. On the contrary, other writers found the expressions convenient and adopted them. They will be found throughout a series of important papers bearing upon hydrography by Sandström, V. W. Ekman, and Helland-Hansen, and they have, further, been regularly employed in the official publications of the "Conseil permanent International pour l'exploration de la mer" in Copenhagen.

No protests having appeared, I did not scruple to make use of this terminology in my book Dynamic Meteorology and Hydrography, of which the first two volumes have appeared both in English and in German.” Should this book and its annexed numerical tables have given rise to a more extended use of the terminology from year to year, I am no longer able to prevent it.

This system of nomenclature, according to which the millibar = 1,000 dynes per square centimeter, was urged upon meteorologists in 1909 by W Köppen also; and was formally adopted in 1912 for use in aerology.

Marvin adds that Bjerknes actually redefined the unit name 'bar', instead of inventing it. In 1888, a committee of the British Association proposed the name barad for 1 dyne per cm². In 1900, a congress of physicists recommended the name 'barye' for 1 dyne per cm², although the original proposal was to use it for 1 megadyne per cm². In 1903 Richards and Kennely** shortened the unit name to bar. Many meteorologists kept using to the old non-CGS pressure units, mm Hg and atmosphere. Bjerknes was the first influential meteorologist/oceanographer to adopt the CGS system, but he redefined the bar to 1 megadyne per cm². Consequently, 1 bar was conveniently close to 1 atmosphere.

* Bjerkness V. & Sandstrom J.W., Beitr. z. Phys. d. freien Atmosphäre, 1906, 2:1. Bjerknes writes: "Da unser Ziel eine weitergehende Diskussion der Dynamik der Atmosphäre ist, können wir uns nur mit absoluter Masse bedienen. Daher muss die gewöhnliche irrationelle Druckeinheit, das mm Hg, aufgeben und durch eine entsprechende, dem absoluten Massasysteme angehorende Einheit ersetzt werden. Als solche praktische Einheit ist oft die Megadyne pro Quadratzentimeter vorgeschlagen worden. Diese Einheit werden wir ein Bar nennen. Das Bar wird in Dezi-, Zenti-, und Millibar geteilt, und das Millibar ersetzt das mm Hg. Das Millibar beträgt sehr nahe 3/4 oder genauer 0.75006 mm Hg."

** Comments by Kennely here. He tried to save the definition of the physicists that 1 bar = 1 dyne per cm² by proposing a different abbreviation for the 'bar of Bjerkness', Bjer, so that 1 Bjer = 1 megabar, but alas, it was too late, nobody listened.

Ceinturion (talk) 22:53, 21 July 2016 (UTC)

Ocean dbar—m unit conversion

From section Bar_(unit)#Usage:

an increase of 1 decibar occurs for every 1.019716 m increase in depth

However, the "check value" in the UNESCO paper (chapter 4) is inconsistent with this. It states that 9712.653 m corresponds with 10000 dbar (at 30°N). This would correspond met approximately 0.97 m/dbar, and in any case for all the numbers in the table on p. 28 is must have a magnitude that is smaller than one. I don't understand where the value 1.019716 comes from (it's not the reciprocal). — Preceding unsigned comment added by Hulten (talk • contribs) 19:43, 19 June 2017 (UTC)

Quoting from the same section, but with more context:

In fresh water, there is an approximate numerical equivalence between the change in pressure in decibars and the change in depth from the water surface in metres. Specifically, an increase of 1 decibar occurs for every 1.019716 m increase in depth.

The latter half of the paragraph starts "In sea water ...", and the UNESCO paper is Algorithms for computation of fundamental properties of seawater. Seawater is roughly 3% denser than fresh water, and the remainder of the 4.8% difference in the figures is largely due to the slight compressibility of water, which becomes quite measurable at the ~ 10 km depth of the check value. -- ToE 16:10, 28 December 2018 (UTC)

That said, the 1.019716 m/decibar figure is troubling both because it is unreferenced and because it is overly precise. It is exactly the value of h/P derived from P=ρgh using g = g₀ = 9.80665 m/s² and ρ = 1.000000 g/cm³. Maximum density of distilled water is 0.999972 g/cm3 at 3.984 °C (see Water (data page)#Liquid physical properties), which gives h/P = 1.019745 m/decibar; ρ = 0.9997026 g/cm3 (10 °C), gives 1.020020 m/decibar; ρ = 0.9991026 g/cm3 (15 °C), gives 1.020632 m/decibar; ρ = 0.9982071 g/cm3 (20 °C), gives 1.021548 m/decibar.

I'm tempted to change it to say "... an increase of 1 decibar occurs for every 1.02 m increase in depth." and leave it at that. h/P wouldn't hit 1.025 m/decibar until ρ = 0.994845 g/cm3 at about 32.5 °C. Plus this is ignoring the ~0.5% latitudinal variation in g. Six significant figures is insane unless the very specific conditions are stated. -- ToE 21:58, 28 December 2018 (UTC)

Plural of bar = bars

I think it would be nice to settle that. That's what I came on this page to look for. I found the answer here: https://forum.tz-uk.com/showthread.php?7413-What-s-the-plural-of-Bar-(as-in-pressure)&s=b0611d225f2b1d7f0331ba8cb4d6669f&p=82226&viewfull=1#post82226

The article is mostly consistent with "millibars" -- but some sections mention "bar" in plural, which I think should be corrected. — Preceding unsigned comment added by 65.125.206.230 (talk) 20:19, 21 February 2019 (UTC)

Bar is a metric unit, but not SI, so it doesn't necessarily follow these conventions. Indeed it seems like the plural "bar" is standard in some contexts, for example this article on rocket engine chamber pressures, as well as wikipedia's own article on that same engine -- Madmonk325 (talk) 20:17, 13 June 2020 (UTC)

"unit should not be used for unit"

@PlanetsForLife: I would have said a link to the unit is precisely what should be used for the unit. Can you explain what you meant when stating the contrary? Thanks, Dondervogel 2 (talk) 11:11, 25 August 2021 (UTC)

Oh, I meant like SI unit for pascals which is also a unit. The link for SI unit should not be the same for pascal (for obvious reasons) so the Atmospheres link should not link to atm unit, something link atmosphere of earth or barometric pressure. Sorry for the confusion. PlanetsForLife 01:18, 26 August 2021 (UTC)

That helps, thanks. Perhaps there should be another (more general) category of units then. Would "Other" be a better category than "Atmospheres"? Dondervogel 2 (talk) 10:26, 26 August 2021 (UTC)

"Dbar" listed at Redirects for discussion

The redirect Dbar has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at Wikipedia:Redirects for discussion/Log/2024 April 26 § Dbar until a consensus is reached. 1234qwer1234qwer4 21:39, 26 April 2024 (UTC)