Ambient pressure

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The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, in contact with the object.

Video Ambient pressure

Atmosphere

Within the atmosphere, the ambient pressure decreases as height increases. By measuring ambient atmospheric pressure, a pilot may determine altitude (see pitot-static system). Near sea level, a change of ambient pressure of 1 millibar is taken to represent a change of height of 9 metres (30 ft).

Maps Ambient pressure

Underwater

The ambient pressure in water with a free surface is a combination of the hydrostatic pressure due to the weight of the water column and the atmospheric pressure on the free surface. This increases approximately linearly with depth. Since water is much denser than air, much greater changes in ambient pressure can be experienced under water. Each 10 metres (33 ft) of depth adds another bar to the ambient pressure.

Ambient pressure diving is underwater diving exposed to the water pressure at depth, rather than in a pressure-excluding atmospheric diving suit or a submersible.

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Other environments

The concept is not limited to environments frequented by people. Almost any place in the universe will have an ambient pressure, from the hard vacuum of deep space to the interior of an exploding supernova. At extremely small scales the concept of pressure becomes irrelevant, and it is undefined at a gravitational singularity.

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Units of pressure

The SI unit of pressure is the pascal (Pa), which is a very small unit relative to atmospheric pressure on Earth, so kilopascals (kPa) are more commonly used in this context. The ambient atmospheric pressure at sea level is not constant: it varies with the weather, but averages around 100 kPa. In fields such as meteorology and underwater diving, it is common to see ambient pressure expressed in bar or millibar. One bar is 100 kPa or approximately ambient pressure at sea level. 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.

Examples of ambient pressure in various environments

Pressures are given in terms of the normal ambient pressure experienced by humans -- standard atmospheric pressure at sea level on earth.

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See also

• pressure

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References

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Further reading

• Frost, David Lawrence; Sturtevant, Bradford (1986). "Effects of ambient pressure on the instability of a liquid boiling explosively at the superheat limit". Journal of Heat Transfer. Caltech Library. 108 (2): 418-24. doi:10.1115/1.3246940. Archived from the original on December 12, 2008. Retrieved 5 January 2010. 
• Damon, Edward G; Gaylord, Charles S; Hicks, William; Yelverton, John T; Richmond, Donald R; White, Clayton S. "The effects of ambient pressure on tolerance of mammals to air blast". Albuquerque: Lovelace Foundation for Medical Education and Research. Retrieved 5 January 2010. 

Source of the article : Wikipedia