| atmospheric pressure ： ウィキペディア英語版|
Atmospheric pressure is the pressure exerted by the weight of air in the atmosphere of Earth (or that of another planet). In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. On a given plane, low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. Likewise, as elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. On average, a column of air one square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kg and weight of about 10.1 N (2.28 lbf). (A column one square inch in cross-section would have a weight of about 14.7 lbs, or about 65.4 N.) Atmospheric pressure is sometimes called barometric pressure.
== Standard atmosphere ==
The standard atmosphere (symbol: atm) is a unit of pressure equal to 101325 Pa〔International Civil Aviation Organization, Manual of the ICAO Standard Atmosphere, Doc 7488-CD, Third Edition, 1993, ISBN 92-9194-004-6.〕 or 1013.25 hectopascals or millibars. Equivalent to 760 mmHg (torr), 29.92 inHg, 14.696 psi. (The pascal is a newton per square meter or in terms of SI base units, kilogram per meter per second-squared.)
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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