AIR PRESSURE

[BSHC]

"Air pressure" redirects here. For the pressure of air in other systems, see pressure.
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Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface 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). Over the area of your body, there is about 1,000 kg of air; this is approximately the same as having a small car press down on you.[1]

The standard atmosphere (symbol: atm) is a unit of pressure equal to 101.325 kPa ("kiloPascals")[2] or 1013.25 millibars or hectopascals. It is equivalent to 760 mmHg (torr), 29.92 inHg, 14.696 psi. One standard is standard pressure used for pneumatic fluid power (ISO R554), and in the aerospace (ISO 2533) and petroleum (ISO 5024) industries. In 1971, the International Union of Pure and Applied Chemistry (IUPAC) said that for the purposes of specifying the properties of substances, "the standard pressure" should be defined as precisely 100 kPa (≈750.01 torr) or 29.53 inHg rather than the 101.325 kPa value of "one standard atmosphere".[3] This value is used as the standard pressure for the compressor and the pneumatic tool industries (ISO 2787).[4] (See also Standard temperature and pressure.) In the United States, compressed air flow is often measured in "standard cubic feet" per unit of time, where the "standard" means the equivalent quantity of air at standard temperature and pressure. For every 300 meters (≈1,000 feet) one ascends, the atmospheric pressure decreases by about 4%. However, this standard atmosphere is defined slightly differently: temperature = 20 °C (68 °F), air density = 1.225 kg/m³ (0.0765 lb/cu ft), altitude = sea level, and relative humidity = 20%. In the air conditioner industry, the standard is often temperature = 0 °C (32 °F) instead. For natural gas, the Gas Processors Association (GPA) specifies a standard temperature of 60 °F (15.6 °C), but allows a variety of "base" pressures, including 14.65 psi (101.0 kPa), 14.656 psi (101.05 kPa), 14.73 psi (101.6 kPa) and 15.025 psi (103.59 kPa).[5] For a given "base" pressure, the higher the air pressure, the colder it is; the lower the air pressure, the warmer it is.

기압을 나타내는 단위로는,

㎜Hg,

pound/in²(psi),

dyne/㎠,

mb, 기압,

kPa

등을 예로 들 수 있다.

정의에 따르면

평균해수면에서의 기압은

760㎜Hg,

14.7 pound/in²,

1,013.25×10³dyne/㎠,

1,013.25mb,

1기압, 혹은 101.35kPa

에 해당한다