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atmospheric pressure
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ATMOSPHERIC PRESSURE

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Alternate titles: air pressure, barometric pressure
By The Editors of Encyclopaedia Britannica • Edit History

--------------------------------------------------------------------------------

Table of Contents
changes in atmospheric pressure with altitude
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Key People: George Dollond ...(Show more) Related Topics: atmosphere barometer
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atmospheric pressure, also called barometric pressure, force per unit area
exerted by an atmospheric column (that is, the entire body of air above the
specified area). Atmospheric pressure can be measured with a mercury barometer
(hence the commonly used synonym barometric pressure), which indicates the
height of a column of mercury that exactly balances the weight of the column of
atmosphere over the barometer. Atmospheric pressure is also measured using an
aneroid barometer, in which the sensing element is one or more hollow, partially
evacuated, corrugated metal disks supported against collapse by an inside or
outside spring; the change in the shape of the disk with changing pressure can
be recorded using a pen arm and a clock-driven revolving drum.

Learn about atmospheric pressure and its units and methods of measurement
Description of pressure and its measurement.
© Josef Martha—sciencemanconsulting.comSee all videos for this article

Atmospheric pressure is expressed in several different systems of units:
millimetres (or inches) of mercury, pounds per square inch (psi), dynes per
square centimetre, millibars (mb), standard atmospheres, or kilopascals.
Standard sea-level pressure, by definition, equals 760 mm (29.92 inches) of
mercury, 14.70 pounds per square inch, 1,013.25 × 103 dynes per square
centimetre, 1,013.25 millibars, one standard atmosphere, or 101.325 kilopascals.
Variations about these values are quite small; for example, the highest and
lowest sea-level pressures ever recorded are 32.01 inches (in the middle of
Siberia) and 25.90 inches (in a typhoon in the South Pacific). The small
variations in pressure that do exist largely determine the wind and storm
patterns of Earth.


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Know why suction cups do not work in outer space
Learn why the lack of atmospheric pressure in the vacuum of space makes suction
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Near Earth’s surface the pressure decreases with height at a rate of about 3.5
millibars for every 30 metres (100 feet). However, over cold air the decrease in
pressure can be much steeper because its density is greater than warmer air. The
pressure at 270,000 metres (10−6 mb) is comparable to that in the best man-made
vacuum ever attained. At heights above 1,500 to 3,000 metres (5,000 to 10,000
feet), the pressure is low enough to produce mountain sickness and severe
physiological problems unless careful acclimatization is undertaken.


January average atmospheric temperature
Global mean air pressure at sea level in January, where high-pressure centres
are more diffuse. Central Asia, however, is dominated by a strong high-pressure
cell.
Encyclopædia Britannica, Inc.

July average atmospheric temperature
Global mean air pressure at sea level in July, where high-pressure centres are
more pronounced, especially over the North Atlantic and North Pacific oceans.
Encyclopædia Britannica, Inc.
The Editors of Encyclopaedia BritannicaThis article was most recently revised
and updated by John P. Rafferty.



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External Websites
 * Hyperphysics - Atmospheric Pressure Examples
 * LiveScience - Atmospheric Pressure: Definition and Facts

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Articles from Britannica Encyclopedias for elementary and high school students.
 * atmospheric pressure - Student Encyclopedia (Ages 11 and up)

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some discrepancies. Please refer to the appropriate style manual or other
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Select Citation Style
MLA APA Chicago Manual of Style
Britannica, The Editors of Encyclopaedia. "atmospheric pressure". Encyclopedia
Britannica, 11 Jan. 2021,
https://www.britannica.com/science/atmospheric-pressure. Accessed 14 April 2022.
Copy Citation
External Websites
 * Hyperphysics - Atmospheric Pressure Examples
 * LiveScience - Atmospheric Pressure: Definition and Facts

Britannica Websites
Articles from Britannica Encyclopedias for elementary and high school students.
 * atmospheric pressure - Student Encyclopedia (Ages 11 and up)



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