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)
[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:
Meters to Millibars
h = height in meters p = pressure in millibars
David Mitchell 22:06, 27 February 2006 (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)
