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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 ]
The International Standard Atmosphere (ISA) is a static atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes or elevations. It has been established to provide a common reference for temperature and pressure and consists of tables of values at various altitudes ...
The U.S. Standard Atmosphere is a static atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes or elevations. The model, based on an existing international standard, was first published in 1958 by the U.S. Committee on Extension to the Standard Atmosphere, and ...
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.
Lung air pressure difference moving the normal breaths of a person (only 0.3% of standard atmospheric pressure) [35] [36] 400–900 Pa 0.06–0.13 psi Atmospheric pressure on Mars, < 1% of atmospheric sea-level pressure on Earth [37] 610 Pa 0.089 psi Partial vapor pressure at the triple point of water (611.657 Pa) [38] [39] 10 3 Pa
Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather . If the entire mass of the atmosphere had a uniform density equal to sea-level density (about 1.2 kg/m 3 ) from sea level upwards, it would terminate abruptly at an altitude of 8.50 ...
When these fluctuations were explained as a manifestation of changes in atmospheric pressure, the science of meteorology was born. Over time, 760 millimeters of mercury at 0 °C came to be regarded as the standard atmospheric pressure. In honour of Torricelli, the torr was defined as a unit of pressure equal to one millimeter of mercury at 0 °C.
Atmospheric air pressure where standard atmospheric pressure is defined as 1013.25 mbar, 101.325 kPa, 1.01325 bar, which is about 14.7 pounds per square inch. Despite the millibar not being an SI unit, meteorologists and weather reporters worldwide have long measured air pressure in millibar as the values are convenient.