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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.
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]
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.
The basic assumptions made for the 1962 version were: [3] air is a clean, dry, perfect gas mixture (c p /c v = 1.40) molecular weight to 90 km of 28.9644 (C-12 scale); principal sea-level constituents are assumed to be (in mole percent):
A torr was originally defined as 1 mmHg. The pressure is quoted as the level of the mercury's height in the vertical column. Typically, atmospheric pressure is measured between 26.5 inches (670 mm) and 31.5 inches (800 mm) of Hg. One atmosphere (1 atm) is equivalent to 29.92 inches (760 mm) of mercury.
Blood pressure fluctuation (40 mmHg) between heartbeats for a typical healthy adult [44] [45] 6.3 kPa 0.9 psi Pressure where water boils at normal human body temperature (37 °C), the pressure below which humans absolutely cannot survive (Armstrong limit) [46] +9.8 kPa +1.4 psi Lung pressure that a typical person can exert (74 mmHg) [47] 10 4 Pa
The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N/m 2, or kg·m −1 ·s −2). This name for the unit was added in 1971; [6] before that, pressure in SI was expressed in newtons per square metre. Other units of pressure, such as pounds per square inch (lbf/in 2) and bar, are also in common use.
760 mmHg = 1 atm; 1 atm = 1 013 mbar or hPa; 1 mbar or hPa = 0.7502467 mmHg; 1 pascal = 1 Newton per square metre (SI unit) 1 hectopascal is 100 pascals Additional images