Talk:Bar (unit)

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The bar is defined as:

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

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)

Contents

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)