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Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2]
It is defined as the pressure exerted by a column of water of 1 inch in height at defined conditions. At a temperature of 4 °C (39.2 °F) pure water has its highest density (1000 kg/m 3). At that temperature and assuming the standard acceleration of gravity, 1 inAq is approximately 249.082 pascals (0.0361263 psi). [2]
The standard atmosphere was originally defined as the pressure exerted by a 760 mm column of mercury at 0 °C (32 °F) and standard gravity (g n = 9.806 65 m/s 2). [2] It was used as a reference condition for physical and chemical properties, and the definition of the centigrade temperature scale set 100 °C as the boiling point of water at this pressure.
Convert mmHg to SI units as follows: 1 mmHg = 0.133 32 kPa. Hence the normal blood pressure in SI units is less than 16.0 kPa SBP and less than 10.7 kPa DBP. These values are similar to the pressure of water column of average human height; so pressure has to be measured on arm roughly at the level of the heart.
Mercury barometer. A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high. . Currently, it is defined as exactly 133.322 387 415 pascals, or approximately 1 torr ( = = , =
Standard sea-level conditions (SSL), [1] also known as sea-level standard (SLS), defines a set of atmospheric conditions for physical calculations.The term "standard sea level" is used to indicate that values of properties are to be taken to be the same as those standard at sea level, and is done to define values for use in general calculations.
Ambient pressure may in other circumstances be measured in pounds per square inch (psi) or in standard atmospheres (atm). The ambient pressure at sea level is approximately one atmosphere, which is equal to 1.01325 bars (14.6959 psi), which is close enough for bar and atm to be used interchangeably in many applications.
atm ccs [citation needed] ≡ 1 atm × 1 cm 3 /s = 0.101 325 W: atmosphere-cubic foot per hour: atm cfh [citation needed] ≡ 1 atm × 1 cu ft/h = 0.797 001 247 04 W: atmosphere-cubic foot per minute: atm cfm [citation needed] ≡ 1 atm × 1 cu ft/min = 47.820 074 682 24 W: atmosphere-cubic foot per second: atm cfs [citation needed] ≡ 1 atm ...