Atmospheric pressure Atmospheric pressure is the pressure caused by the weight of air above any area in the Earth's atmosphere. Standard atmospheric pressure (atm) is discussed in the next section. Air masses are affected by the general atmospheric pressure within the mass, creating areas of high and low pressure. As elevation increases, fewer air molecules are above. Therefore, atmospheric pressure decreases with increasing height. The following relationship is a first-order approximation: $\backslash log\_\; P\; \backslash approx\; \}$, where P is the pressure in pascals and h the height in metres. This shows that the pressure at an altitude of 31 km is about 1% of that at sea level. [Source: US Department of Defense Military Standard 810E] A column of air, 1 square inch in cross section, measured from sea level to the top of the atmosphere would weigh approximately 14.7 lb. A 1 m2 column of air would weigh about 10 tonnes. See density of air. Standard atmospheric pressure Standard atmospheric pressure or "the standard atmosphere" (1 atm) is defined as 101.325 kPa. (see also Standard temperature and pressure) This can also be stated as: 29.92 inches of mercury 760 mm of mercury 760 torr 1013.25 millibars (mb) 14.7 psia or 0 psig 0.967838490064855 at (metric atmospheric pressure). This "standard pressure" is a purely arbitrary representative value for pressure at sea level, and real atmospheric pressures vary from place to place and moment to moment everywhere in the world. In a low atmospheric pressure system the atmospheric pressure of the air mass is lower than that of the surrounding air. Low atmospheric pressure systems are symbolized by an L on a weather map and are associated with areas of storminess and precipitation. Wind movement is cyclonic around a low pressure system and cold fronts and warm fronts are generally connected to them. In a high atmospheric pressure system the atmospheric pressure of the air mass is higher than that of the surrounding air. High atmospheric pressure systems are symbolized by an H on a weather map and are associated with areas of clear weather. It is possible to demonstrate atmospheric pressure in a classroom or home environment using the crushing can experiment. See Atmospheric pressure demo See also plenum NRLMSISE-00 External links An exercise in air pressure Calculations and conversions of pressure units Conversions of pressure or stress units Most Popular Articles: Music    Musical Instruments    Guitar    Classical Music    History    Music Definition    Country Music    Rock Music    Pop Music    Hip Hop    Rap    DJ    Video Games    Casino Games    Poker    Blackjack    Casinos    Real Estate    Loan    Auction    eBay    Marketing    Search Engine Optimization    File Sharing    MP3    Music Industry    Kazaa    Internet    Supermodel    Fashion    Fashion Designers    Erotica    Modeling    Clothing    Boots    Shoes    Diamond Engagement Rings    Diamond    Rugs    Gospel Music    Affiliate    E-Commerce    Radio This article is licensed under the GNU Free Documentation License at http://www.gnu.org/copyleft/fdl.html You may copy and modify it as long as the entire work (including additions) remains under this license. You must provide a link to http://www.gnu.org/copyleft/fdl.html To view or edit this article at Wikipedia go to http://www.wikipedia.org/wiki/Atmospheric_pressure