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= molar mass of Earth's air: 0.0289644 kg/mol The value of subscript b ranges from 0 to 6 in accordance with each of seven successive layers of the atmosphere shown in the table below. The reference value for ρ b for b = 0 is the defined sea level value, ρ 0 = 1.2250 kg/m 3 or 0.0023768908 slug/ft 3 .
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 ]
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.
at each geopotential altitude, where g is the standard acceleration of gravity, and R specific is the specific gas constant for dry air (287.0528J⋅kg −1 ⋅K −1). The solution is given by the barometric formula. Air density must be calculated in order to solve for the pressure, and is used in calculating dynamic pressure for moving vehicles.
Pressure units Pascal Bar Technical atmosphere Standard atmosphere Torr Pound per square inch (Pa) (bar) (at) (atm) (Torr) (lbf/in 2) 1 Pa — 1 Pa = 10 −5 bar
T = mean atmospheric temperature in kelvins = 250 K [4] for Earth m = mean mass of a molecule M = mean molar mass of atmospheric particles = 0.029 kg/mol for Earth g = acceleration due to gravity at the current location. The pressure (force per unit area) at a given altitude is a result of the weight of the overlying atmosphere.
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