View source for Physics:Atmospheric pressure

{{short description|Static pressure exerted by the weight of the atmosphere }}
'''Atmospheric pressure''', also known as '''barometric pressure''' (after the [[Engineering:Barometer|barometer]]),    is the [[Physics:Pressure|pressure]] within the [[Earth:Atmosphere of Earth|atmosphere of Earth]]. The [[Physics:Standard atmosphere (unit)|standard atmosphere]] (symbol: atm) is a unit of pressure defined as {{cvt|101325|Pa|hPa|lk=on}}, which is equivalent to 1,013.25 [[Bar (unit)|millibars]],<ref>{{cite web|url=https://www.bipm.org/en/committees/ci/cipm/90-2001/resolution- |title=Statement (2001) |publisher=BIPM |date= |accessdate=2022-03-19}}</ref> 760{{nbsp}}[[Physics:Millimetre of mercury|mm Hg]], 29.9212{{nbsp}}[[Inch of mercury|inches{{nbsp}}Hg]], or 14.696{{nbsp}}[[Pounds per square inch|psi]].<ref name="ICAO">International Civil Aviation Organization. ''Manual of the [[International Standard Atmosphere|ICAO Standard Atmosphere]]'', Doc 7488-CD, Third Edition, 1993. {{ISBN|92-9194-004-6}}.</ref> The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.

In most circumstances, atmospheric pressure is closely approximated by the hydrostatic pressure caused by the [[Physics:Weight|weight]] of air above the measurement point. As [[Elevation|elevation]] increases, there is less overlying atmospheric mass, so atmospheric pressure decreases with increasing elevation. Because the atmosphere is thin relative to the Earth's radius—especially the dense atmospheric layer at low altitudes—the Earth's [[Physics:Gravitational acceleration|gravitational acceleration]] as a function of altitude can be approximated as constant and contributes little to this fall-off. Pressure measures force per unit area, with [[International System of Units|SI units]] of [[Pascal (unit)|pascals]] (1 pascal = 1 [[Newton (unit)|newton]] per square [[Metre|metre]], 1{{nbsp}}N/m<sup>2</sup>). On average, a column of air with a cross-sectional area of 1 square [[Centimetre|centimetre]] (cm<sup>2</sup>), measured from the mean (average) sea level to the top of Earth's atmosphere, has a [[Physics:Mass|mass]] of about 1.03 [[Kilogram|kilogram]] and exerts a [[Physics:Force|force]] or "weight" of about 10.1 newtons, resulting in a pressure of 10.1 N/cm<sup>2</sup> or 101{{nbsp}}[[Newton (unit)#Kilonewtons|kN]]/m<sup>2</sup> (101 kilopascals, kPa). A column of air with a cross-sectional area of 1{{nbsp}}in<sup>2</sup> would have a weight of about 14.7{{nbsp}}[[Pound (force)|lbf]], resulting in a pressure of 14.7{{nbsp}}lbf/in<sup>2</sup>.

==Mechanism==
<!--what causes atmospheric pressure-->
Atmospheric pressure is caused by the gravitational attraction of the planet on the atmospheric gases above the surface and is a function of the mass of the planet, the radius of the surface, and the amount and composition of the gases and their vertical distribution in the atmosphere.<ref>{{cite magazine|title=atmospheric pressure (encyclopedic entry)|url=https://www.nationalgeographic.org/encyclopedia/atmospheric-pressure/|magazine=National Geographic|access-date=28 February 2018|archive-date=28 February 2018|archive-url=https://web.archive.org/web/20180228194703/https://www.nationalgeographic.org/encyclopedia/atmospheric-pressure/|url-status=live}}</ref><ref>{{cite web|title=Q & A: Pressure – Gravity Matters?|url=https://van.physics.illinois.edu/qa/listing.php?id=2232|website=Department of Physics|publisher=University of Illinois Urbana-Champaign|access-date=28 February 2018|archive-date=28 February 2018|archive-url=https://web.archive.org/web/20180228194620/https://van.physics.illinois.edu/qa/listing.php?id=2232|url-status=live}}</ref> It is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition.<ref>{{Cite book|url=https://books.google.com/books?id=14whM9fEOzsC&q=atmospheric+pressure+density+temperature+and+composition|title=Introduction to Atmospheric Chemistry|last=Jacob|first=Daniel J.|date=1999|publisher=Princeton University Press|isbn=9780691001852|language=en|access-date=2020-10-15|archive-date=2021-10-01|archive-url=https://web.archive.org/web/20211001043009/https://books.google.com/books?id=14whM9fEOzsC&q=atmospheric+pressure+density+temperature+and+composition|url-status=live}}</ref>

== Mean sea-level pressure ==
[[File:Day5pressureforecast.png|thumb|left|Map showing atmospheric pressure in mbar or hPa]]
[[File:Mslp-jja-djf.png|thumb|15-year average mean sea-level pressure for June, July, and August (top) and December, January, and February (bottom). [[Earth:ECMWF re-analysis|ERA-15]] re-analysis.]]
[[File:Aircraft altimeter.JPG|thumb|Kollsman-type barometric aircraft [[Engineering:Altimeter|altimeter]].]]

The ''mean sea-level pressure'' (MSLP) is the atmospheric pressure at mean sea level (PMSL). This is the atmospheric pressure normally given in weather reports on radio, television, and newspapers or on the [[Internet]]. When [[Engineering:Barometer|barometer]]s in the home are set to match the local weather reports, they display pressure adjusted to sea level, not the actual local atmospheric pressure.

The ''altimeter setting'' in aviation is an atmospheric pressure adjustment.

Average ''sea-level pressure'' is {{cvt|1013.25|hPa|inHg mmHg}}. In aviation weather reports ([[METAR]]), QNH is transmitted around the world in hectopascals or millibars  (1 hectopascal = 1 millibar), except in the {{wipe|United States}}, {{wipe|Canada}}, and {{wipe|Japan}} where it is reported in inches of mercury (to two decimal places). The United States and Canada also report ''sea-level pressure'' SLP, which is adjusted to sea level by a different method, in the remarks section, not in the internationally transmitted part of the code, in hectopascals or millibars.<ref>[http://www.flightplanning.navcanada.ca/cgi-bin/Fore-obs/metar.cgi?NoSession=NS_Inconnu&format=dcd&Langue=anglais&Region=can&Stations=CYVR&Location= Sample METAR of CYVR] {{Webarchive|url=https://web.archive.org/web/20190525162442/https://flightplanning.navcanada.ca/cgi-bin/Fore-obs/metar.cgi?NoSession=NS_Inconnu&format=dcd&Langue=anglais&Region=can&Stations=CYVR&Location= |date=2019-05-25 }} Nav Canada</ref> However, in Canada's public weather reports, sea level pressure is instead reported in kilopascals.<ref>{{citation |url=http://www.cbc.ca/montreal/weather/s0000635.html |title=Montreal Current Weather |publisher=CBC Montreal, Canada |access-date=2014-03-30 |archive-date=2014-03-30 |archive-url=https://web.archive.org/web/20140330055543/http://www.cbc.ca/montreal/weather/s0000635.html |url-status=live }}</ref>

In the US weather code remarks, three digits are all that are transmitted; decimal points and the one or two most significant digits are omitted: {{cvt|1013.2|hPa}}  is transmitted as 132; {{cvt|1000|hPa|kPa}} is transmitted as 000; 998.7{{nbsp}}hPa is transmitted as 987; etc. The highest ''sea-level pressure'' on [[Astronomy:Earth|Earth]] occurs in Siberia, where the Siberian High often attains a ''sea-level pressure'' above {{cvt|1050|hPa|psi inHg}}, with record highs close to {{cvt|1085|hPa|psi inHg}}. The lowest measurable ''sea-level pressure'' is found at the centres of [[Physics:Tropical cyclone|tropical cyclone]]s and [[Earth:Tornado|tornado]]es, with a [[Physics:Atmospheric pressure#Records|record low]] of {{cvt|870|hPa|psi inHg|comma=off}}.

== Surface pressure {{anchor|Surface}} ==

''Surface pressure'' is the atmospheric pressure at a location on [[Astronomy:Earth|Earth]]'s surface ([[Terrain|terrain]] and oceans).  It is directly proportional to the [[Physics:Mass|mass]] of air over that location.

For numerical reasons, atmospheric models such as [[Earth:General circulation model|general circulation model]]s (GCMs) usually predict the nondimensional ''[[Logarithm|logarithm]] of surface pressure''.

The average value of surface pressure on Earth is 985 hPa.<ref name="jacobs">Jacob, Daniel J. [https://books.google.com/books?id=7B8EEn_sj0cC&q=%22surface+pressure%22 Introduction to Atmospheric Chemistry] {{Webarchive|url=https://web.archive.org/web/20200725014305/https://books.google.com/books?id=7B8EEn_sj0cC&printsec=frontcover#v=onepage&q=%22surface%20pressure%22&f=false |date=2020-07-25 }}. Princeton University Press, 1999.</ref> This is in contrast to mean sea-level pressure, which involves the extrapolation of pressure to sea level for locations above or below sea level. The average pressure at mean sea level (MSL) in the International Standard Atmosphere ([[International Standard Atmosphere|ISA]]) is 1,013.25 hPa, or 1 atmosphere (atm), or 29.92 inches of mercury.

Pressure (P), mass (m), and acceleration due to gravity (g) are related by P = F/A = (m*g)/A, where A is the surface area. Atmospheric pressure is thus proportional to the weight per unit area of the atmospheric mass above that location.

== Altitude variation ==
{{further|Barometric formula|Vertical pressure variation}}
[[File:Storm over Snæfellsjökull.jpg|thumb|left|A very local storm above [[Earth:Snæfellsjökull|Snæfellsjökull]] (Iceland), showing clouds formed on the mountain by orographic lift]]
[[File:Atmospheric Pressure vs. Altitude.png|thumb|300px|Variation in atmospheric pressure with altitude, computed for 15&nbsp;°C and 0% relative humidity.]]
[[File:Plastic bottle at 14000 feet, 9000 feet and 1000 feet, sealed at 14000 feet.png|thumb|This plastic bottle was sealed at approximately {{convert|14000|ft|m|disp=flip}} altitude, and was crushed by the increase in atmospheric pressure, recorded at {{convert|9000|ft|m|disp=flip}} and {{convert|1000|ft|m|disp=flip}}, as it was brought down towards sea level.]]

Pressure on Earth varies with the altitude of the surface, so air pressure on mountains is usually lower than air pressure at sea level. Pressure varies smoothly from the Earth's surface to the top of the [[Earth:Mesosphere|mesosphere]]. Although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases. One can calculate the atmospheric pressure at a given altitude.<ref>[http://archive.psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdf A quick derivation relating altitude to air pressure] {{webarchive|url=https://web.archive.org/web/20110928003908/http://psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdf |archive-url=https://web.archive.org/web/20100614221022/http://psas.pdx.edu/RocketScience/PressureAltitude_Derived.pdf |archive-date=2010-06-14 |url-status=live |date=2011-09-28 }} by Portland State Aerospace Society, 2004, accessed 05032011</ref> Temperature and humidity also affect the atmospheric pressure. Pressure is proportional to temperature and inversely proportional to humidity. And it is necessary to know both of these to compute an accurate figure. The graph {{if mobile|above|on the right}} was developed for a temperature of 15&nbsp;°C and a relative humidity of 0%.

At low altitudes above sea level, the pressure decreases by about {{convert|1.2|kPa|hPa|abbr=on}} for every 100&nbsp; metres. For higher altitudes within the [[Earth:Troposphere|troposphere]], the following equation (the [[Barometric formula|barometric formula]]) relates atmospheric pressure ''p'' to altitude ''h'':
<math>\begin{align}
  p &=       p_0 \cdot \left(1 - \frac{L \cdot h}{T_0} \right)^\frac{g \cdot M}{R_0 \cdot L} \\
    &= p_0 \cdot \left(1 - \frac{g \cdot h}{c_\text{p} \cdot T_0} \right)^{\frac{c_\text{p} \cdot M}{R_0}}
       \approx p_0 \cdot \exp \left(-\frac{g \cdot h \cdot M}{T_0 \cdot R_0} \right)
\end{align}</math>

.  The values in these equations are:
{|class="wikitable sortable"
|-
! Parameter !! Description !! Value
|-
| ''h'' || style="text-align:left;"| Height above mean sea level || style="text-align:right;" | {{nbsp}}m
|-
| ''p''<sub>0</sub> || style="text-align:left;"| Sea level standard atmospheric pressure || style="text-align:right;"| 101,325{{nbsp}}Pa
|-
| ''L'' || style="text-align:left;"| Temperature lapse rate, = ''g''/''c''<sub>p</sub> for dry air || style="text-align:right;"| ~ 0.00976{{nbsp}}K/m
|-
| ''c''<sub>p</sub> || style="text-align:left;"| Constant-pressure specific heat || style="text-align:right;"| 1,004.68506{{nbsp}}J/(kg·K)
|-
| ''T''<sub>0</sub>|| style="text-align:left;"| Sea level standard temperature || style="text-align:right;"| 288.16{{nbsp}}K
|-
| ''g'' || style="text-align:left;"| Earth-surface gravitational acceleration || style="text-align:right;"| 9.80665{{nbsp}}m/s<sup>2</sup>
|-
| ''M'' || style="text-align:left;"| Molar mass of dry air || style="text-align:right;"| 0.02896968{{nbsp}}kg/mol
|-
| ''R''<sub>0</sub> || style="text-align:left;"| Universal gas constant || style="text-align:right;"| 8.314462618{{nbsp}}J/(mol·K)
|}

== Local variation ==
[[File:Wilma1315z-051019-1kg12.jpg|thumb|Hurricane Wilma on 19 October 2005. The pressure in the eye of the storm was {{convert|882|hPa|abbr=on}} at the time the image was taken.]]
Atmospheric pressure varies widely on Earth, and these changes are important in studying [[Earth:Weather|weather]] and [[Earth:Climate|climate]]. Atmospheric pressure shows a diurnal or semidiurnal (twice-daily) cycle caused by global atmospheric tides. This effect is strongest in tropical zones, with an amplitude of a few hectopascals, and almost zero in polar areas. These variations have two superimposed cycles, a circadian (24&nbsp;h) cycle, and a semi-circadian (12&nbsp;h) cycle.

== Records ==
The highest adjusted-to-sea level barometric pressure ever recorded on Earth (above 750 meters) was {{convert|1084.8|hPa|inHg|abbr=on}} measured in Tosontsengel, Mongolia on 19 December 2001.<ref name="wmo.ASU.edu">{{citation|url=http://wmo.asu.edu/highest-sea-lvl-air-pressure-above-700m |title=World: Highest Sea Level Air Pressure Above 750&nbsp;m |publisher=Wmo.asu.edu |date=2001-12-19 |access-date=2013-04-15 |url-status=dead |archive-url=https://web.archive.org/web/20121017130834/http://wmo.asu.edu/highest-sea-lvl-air-pressure-above-700m |archive-date=2012-10-17 }}</ref> The highest adjusted-to-sea level barometric pressure ever recorded (below 750 meters) was at Agata in Evenk Autonomous Okrug, Russia (66°53'{{nbsp}}N, 93°28'{{nbsp}}E, elevation: {{convert|261|m|abbr=on|disp=comma}}) on 31 December 1968 of {{convert|1083.8|hPa|inHg|3|abbr=on}}.<ref>{{citation|url=http://wmo.asu.edu/world-highest-sea-level-air-pressure-below-700m |title=World: Highest Sea Level Air Pressure Below 750&nbsp;m |publisher=Wmo.asu.edu |date=1968-12-31 |access-date=2013-04-15 |url-status=dead |archive-url=https://web.archive.org/web/20130514175318/http://wmo.asu.edu/world-highest-sea-level-air-pressure-below-700m |archive-date=2013-05-14 }}</ref>  The discrimination is due to the problematic assumptions (assuming a standard lapse rate) associated with reduction of sea level from high elevations.<ref name="wmo.ASU.edu" />

The [[Earth:Dead Sea|Dead Sea]], the lowest place on Earth at {{convert|430|m}} below sea level, has a correspondingly high typical atmospheric pressure of 1,065{{nbsp}}hPa.<ref>{{cite journal|last=Kramer |first=MR |author2=Springer C |author3=Berkman N |author4=Glazer M |author5=Bublil M |author6=Bar-Yishay E |author7=Godfrey S |title=Rehabilitation of hypoxemic patients with COPD at low altitude at the Dead Sea, the lowest place on earth |journal=Chest |date=March 1998 |volume=113 |issue=3 |pages=571–575 |url=http://journal.publications.chestnet.org/data/Journals/CHEST/21761/571.pdf |doi=10.1378/chest.113.3.571 |pmid=9515826 |url-status=dead |archive-url=https://web.archive.org/web/20131029195349/http://journal.publications.chestnet.org/data/Journals/CHEST/21761/571.pdf |archive-date=2013-10-29 }}</ref> A below-sea-level surface pressure record of {{convert|1081.8|hPa|inHg|abbr=on}} was set on 21 February 1961.<ref>{{cite journal |last=Court |first=Arnold |year=1969 |title=Improbable Pressure Extreme: 1070 Mb. |journal=Bulletin of the American Meteorological Society |volume=50 |issue=4 |pages=248–50 |jstor=26252600 }}</ref>

The lowest non-tornadic atmospheric pressure ever measured was 870&nbsp;hPa (0.858&nbsp; atm; 25.69&nbsp;inHg), set on 12 October 1979, during Typhoon Tip in the western Pacific Ocean. The measurement was based on an instrumental observation made from a reconnaissance aircraft.<ref name=FAQ1>{{cite web|url=http://www.aoml.noaa.gov/hrd/tcfaq/E1.html |title=Subject: E1), Which is the most intense tropical cyclone on record? |author=Chris Landsea|publisher=[[Organization:Atlantic Oceanographic and Meteorological Laboratory|Atlantic Oceanographic and Meteorological Laboratory]]|date=2010-04-21 |access-date=2010-11-23| archive-url= https://web.archive.org/web/20101206200600/http://www.aoml.noaa.gov/hrd/tcfaq/E1.html| archive-date= 6 December 2010 | url-status= live}}</ref>

== Measurement based on the depth of water ==
One [[Physics:Atmosphere (unit)|atmosphere]] ({{cvt|101.325|kPa|psi|disp=or|1}}) is also the pressure caused by the weight of a column of freshwater of approximately {{cvt|10.3|m|ft|1}}. Thus, a diver 10.3&nbsp;m underwater experiences a pressure of about 2 atmospheres (1&nbsp;atm of air plus 1&nbsp;atm of water). Conversely, 10.3&nbsp;m is the maximum height to which water can be raised using [[Physics:Suction|suction]] under standard atmospheric conditions.

Low pressures, such as [[Chemistry:Natural gas|natural gas]] lines, are sometimes specified in [[Physics:Inch of water|inches of water]], typically written as ''w.c.'' (water column) gauge or ''w.g.'' (inches water) gauge. A typical gas-using residential appliance in the US is rated for a maximum of {{cvt|1/2|psi|kPa mbar}}, which is approximately 14&nbsp;w.g. Similar metric units with a wide variety of names and notation based on [[Physics:Millimeters, water gauge|millimetres]], [[Physics:Centimetre of water|centimetres]] or metres are now less commonly used.

== Boiling point of liquids ==
[[File:Kochendes wasser02.jpg|thumb|Boiling water]]
Pure water [[Physics:Boiling|boils]] at {{convert|100|C}} at earth's standard atmospheric pressure. The boiling point is the temperature at which the vapour pressure is equal to the atmospheric pressure around the liquid.<ref>{{citation |url=http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/vappre.html |title=Vapour Pressure |publisher=Hyperphysics.phy-astr.gsu.edu |access-date=2012-10-17 |archive-date=2017-09-14 |archive-url=https://web.archive.org/web/20170914100414/http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/vappre.html |url-status=live }}</ref> Because of this, the boiling point of liquids is lower at lower pressure and higher at higher pressure. Cooking at high elevations, therefore, requires adjustments to recipes<ref>{{citation |url=http://www.crisco.com/Cooking_Central/Cooking_Tips/Prep_High_Alt.aspx |title=High Altitude Cooking |publisher=Crisco.com |date=2010-09-30 |access-date=2012-10-17 |url-status=dead |archive-url=https://web.archive.org/web/20120907232429/http://www.crisco.com/Cooking_Central/Cooking_Tips/Prep_High_Alt.aspx |archive-date=2012-09-07 }}</ref> or [[Physics:Pressure cooking|pressure cooking]]. A rough approximation of elevation can be obtained by measuring the temperature at which water boils; in the mid-19th century, this method was used by explorers.<ref>{{cite journal |first1=M. N. |last1=Berberan-Santos |first2=E. N. |last2=Bodunov |first3=L. |last3=Pogliani |title=On the barometric formula |journal=American Journal of Physics |volume=65 |issue=5 |pages=404–412 |year=1997 |doi=10.1119/1.18555 |bibcode = 1997AmJPh..65..404B  }}</ref> Conversely, if one wishes to evaporate a liquid at a lower temperature, for example in [[Distillation|distillation]], the atmospheric pressure may be lowered by using a [[Physics:Vacuum pump|vacuum pump]], as in a [[Organization:Rotary evaporator|rotary evaporator]].

== Measurement and maps ==
An important application of the knowledge that atmospheric pressure varies directly with altitude was in determining the height of hills and mountains, thanks to reliable pressure measurement devices. In 1774, Maskelyne was [[Physics:Schiehallion experiment|confirming Newton's theory of gravitation]] at and on Schiehallion mountain in Scotland, and he needed to measure elevations on the mountain's sides accurately.  William Roy, using barometric pressure, was able to confirm Maskelyne's height determinations, the agreement being to be within one meter (3.28 feet). This method became and continues to be useful for survey work and map making.<ref>Hewitt, Rachel, ''Map of a Nation – a Biography of the Ordnance Survey'' {{ISBN|1-84708-098-7}}</ref>

== See also ==
{{Div col}}
* {{annotated link|Physics:Density of air|Atmospheric density}}
* {{annotated link|Earth:Atmosphere of Earth}}
* {{annotated link|Barometric formula}}
* {{annotated link|Medicine:Barotrauma}} – physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding gas or liquid.
* {{annotated link|Engineering:Cabin pressurization}}
* {{annotated link|Physics:Cavitation}}
* [[Physics:Collapsing can|Collapsing can]] – an aluminium can is crushed by the atmospheric pressure surrounding it
* {{annotated link|Medicine:Effects of high altitude on humans}}
* {{annotated link|Earth:High-pressure area}}
* {{annotated link|International Standard Atmosphere}}, a tabulation of typical variations of principal thermodynamic variables of the atmosphere (pressure, density, temperature, etc.) with altitude, at middle latitudes.
* {{annotated link|Physics:Low-pressure area}}
* {{annotated link|Physics:Meteorology}}
* {{annotated link|Earth:NRLMSISE-00}}, an empirical, global reference atmospheric model of the Earth from ground to space
* {{annotated link|Physics:Pressure}}
* {{annotated link|Physics:Pressure measurement}}
* {{annotated link|Physics:Standard atmosphere (unit)}}
* {{annotated link|Earth:Horse latitudes}}
{{div col end}}

== References ==
{{reflist|30em}}

== External links ==
*[https://earth.nullschool.net/#current/wind/surface/level/overlay=mean_sea_level_pressure/winkel3 Current map of global mean sea-level pressure]
*[https://web.archive.org/web/20060513194709/http://modelweb.gsfc.nasa.gov/atmos/us_standard.html 1976 Standard Atmosphere] from [[Organization:NASA|NASA]]
*[http://www.pdas.com/atmos.html Source code and equations for the 1976 Standard Atmosphere]
*[https://web.archive.org/web/20070310223946/http://www.atmosculator.com/The%20Standard%20Atmosphere.html A mathematical model of the 1976 U.S. Standard Atmosphere]
*[http://www.luizmonteiro.com/StdAtm.aspx Calculator using multiple units and properties for the 1976 Standard Atmosphere]
*[http://www.csgnetwork.com/pressurealtcalc.html Calculator giving standard air pressure at a specified altitude, or altitude at which a pressure would be standard]
*[https://www.herramientasingenieria.com/onlinecalc/altitude/altitude.html Calculate pressure from altitude and vice versa]

=== Experiments ===
*[http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/patm.html#atm Movies on atmospheric pressure experiments from] [[Organization:Georgia State University|Georgia State University]]'s [[Software:QuickTime|HyperPhysics website&nbsp;– requires QuickTime]]
*[http://www.teachertube.com/viewVideo.php?video_id=62613 Test showing a can being crushed after boiling water inside it, then moving it into a tub of ice-cold water.]

{{Meteorological variables}}

[[Category:Atmosphere]]
[[Category:Atmospheric thermodynamics]]
[[Category:Pressure]]
[[Category:Underwater diving physics]]

{{Sourceattribution|Atmospheric pressure|1}}