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| {{Use dmy dates|date=October 2011}}
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| {{Infobox Unit
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| | bgcolour =
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| | name = Pascal
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| | image = [[Image:Psidial.jpg|250px]]
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| | caption = A [[pressure gauge]] reading in [[Pounds per square inch|psi]] (red scale) and kPa (black scale)
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| | standard = [[SI derived unit]]
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| | quantity = [[Pressure]] or [[Stress (physics)|stress]]
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| | symbol = Pa
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| | dimension = M⋅L<sup>−1</sup>⋅T<sup>−2</sup>
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| | namedafter = [[Blaise Pascal]]
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| | extralabel = In [[SI base unit]]s:
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| | extradata = 1 Pa = 1 kg/(m·[[second|s]]<sup>2</sup>)
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| }}
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| The '''pascal''' (symbol: '''Pa''') is the [[International System of Units|SI]] [[SI derived unit|derived unit]] of [[pressure]], [[internal pressure]], [[stress (physics)|stress]], [[Young's modulus]] and [[tensile strength]],<ref>{{SIbrochure8th|page=118}}</ref> named after the French mathematician, physicist, inventor, writer, and philosopher [[Blaise Pascal]]. It is a measure of [[force]] per unit area, defined as one [[Newton (unit)|newton]] per [[square meter]].
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| Common multiple units of the pascal are the '''hectopascal''' (1 '''hPa''' ≡ 100 Pa), '''kilopascal''' (1 '''kPa''' ≡ 1000 Pa), '''megapascal''' (1 '''MPa''' ≡ 1,000,000 Pa), and '''gigapascal''' (1 '''GPa''' ≡ 1,000,000,000 Pa).
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| On Earth, [[Atmosphere (unit)|standard atmospheric pressure]] is 101.325 kPa. [[Meteorology|Meteorological]] [[barometric pressure]] reports typically report atmospheric pressure in hectopascals.<ref>[http://www.ofcm.gov/fmh-1/fmh1.htm U.S. Federal Meteorological Handbook]</ref> The kilopascal is used in other applications such as inflation guidance markings on [[bicycle tyre]]s.<ref>[[ISO 5775]]: Bicycle tires and rims</ref> One hectopascal corresponds to about 0.1% of [[atmospheric pressure]] slightly above sea level; one kilopascal is about 1% of atmospheric pressure. One hectopascal is equivalent to one [[Bar (unit)|millibar]]; one standard [[atmosphere (unit)|atmosphere]] is exactly equal to 101.325 kPa or 1013.25 hPa or 101325 Pa. The corresponding Imperial unit is [[pounds per square inch]] (psi).
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| == Definition ==
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| The pascal can be expressed using [[SI derived unit]]s, or alternatively solely [[SI base unit]]s, as:
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| :<math>{\rm 1~Pa = 1~\frac{N}{m^2} = 1~\frac{kg}{m \cdot s^2}}</math><ref>[http://www.bipm.org/en/si/si_brochure/chapter2/2-2/table3.html Table 3 (Section 2.2.2)], ''SI Brochure'', [[International Bureau of Weights and Measures]]</ref>
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| Where '''N''' is the [[Newton (unit)|newton]], '''m''' is the [[metre]], '''kg''' is the [[kilogram]] and '''s''' is the [[second]].
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| {{SI unit lowercase|Blaise Pascal|pascal|Pa}}
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| {{Pressure Units}}
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| === Origin ===
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| The unit is named after [[Blaise Pascal]], the eminent French [[mathematician]], [[physicist]], and philosopher noted for his experiments with a [[barometer]], an instrument to measure [[air pressure]]. The name '''pascal''' was adopted for the [[SI]] unit [[Newton (unit)|newton]] per square metre (N/m<sup>2</sup>) by the 14th [[CGPM]] in 1971.<ref>[http://www.bipm.fr/en/convention/cgpm/14/pascal-siemens.html bipm.fr]</ref>
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| == Miscellaneous ==
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| [[Atmosphere (unit)|Standard atmospheric pressure]] is 101 325 Pa <br> = 101.325 kPa <br> = 1013.25 hPa <br> = 1.01325 bar <br> = 1013.25 mbar <br> = 0.101325 MPa <br> = 760 [[Torr]]<ref>{{cite web
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| |url = http://www.bipm.org/jsp/en/ViewCGPMResolution.jsp?CGPM=10&RES=4
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| |title = Resolution 4 of the 10th meeting of the CGPM
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| |publisher=[[CGPM|Conférence Générale des Poids et Mesures (CGPM)]]
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| |year = 1954
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| |accessdate =5 April 2010}}</ref> <br> = 14.696 [[Pounds per square inch|psi]]. <br> This definition is used for pneumatic fluid power (ISO R554), and in the aerospace (ISO 2533) and petroleum (ISO 5024) industries.
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| In 1985 the [[IUPAC]] recommended that the standard for atmospheric pressure should be harmonized to 100,000 Pa = 1 [[bar (unit)|bar]] ≈ 750.06 [[Torr]]. The same definition is used in the compressor and the pneumatic tool industries (ISO 2787).
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| The [[Unicode]] computer character set has dedicated symbols {{Unicode|㎩}} ({{U+|33A9}}) for Pa and {{Unicode|㎪}} ({{U+|33AA}}) for kPa, but these exist merely for backward-compatibility with some older ideographic character-sets and are therefore [[deprecate]]d.
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| == Uses ==
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| The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced the [[pounds per square inch]] (psi) unit, except in some countries that still use the [[Imperial measurement system]], including the [[United States of America|United States]].
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| [[Tectonophysics|Tectonophysicists]] use the gigapascal (GPa) in measuring or calculating tectonic forces within the earth.
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| Transient [[elastography]] (FibroScan), a non-invasive method for estimating the extent of liver fibrosis, measures liver stiffness in kilopascals.
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| In [[materials science]], megapascals (MPa = [[Newton (unit)|N]]/mm<sup>2</sup>) or gigapascals (GPa = kN/mm<sup>2</sup>) are commonly used to measure [[Young's modulus|stiffness]] or [[tensile strength]] of materials. Examples of (approximate) Young’s moduli for several common substances (in gigapascals) include [[nylon]] at 2–4; [[hemp]] (fibre) at 58, [[aluminium]] at 69; [[tooth enamel]] at 83, [[copper]] at 117, [[steel]] at approximately 200, and [[diamond]] at 1220.
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| The pascal is also equivalent to the SI unit of [[energy density]], J/m<sup>3</sup>. This applies not only to the thermodynamics of pressurized gasses, but also to the energy density of [[electric potential energy|electric]], [[magnetic field#Energy stored in magnetic fields|magnetic]], and [[gravitational energy|gravitational]] fields.
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| Other, older units of measure occasionally used for pressure are [[millimeters of mercury]] ([[Torr]]) and millimetres of water (1.0 mmH<sub>2</sub>O = 9.80665 Pa).
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| In the [[centimetre-gram-second system of units|cgs system]], the unit of pressure is the [[barye]] (symbol '''ba'''), which is equal to one [[deci-|deci]]pascal. The older kilogram-force per square centimetre corresponds to 98.0665 kPa,<ref>SensorsOne, [http://www.sensorsone.co.uk/pressure-units-conversion.html Pressure unit conversion and converter]. 2010.03.22.</ref> but is it often rounded off to 100 kPa in practice.
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| In the former [[metre-tonne-second system of units|mts system]], the unit of pressure is the [[pièze]] (symbol '''pz'''), which is equal to one kilopascal.
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| [[Blower door|Airtightness testing of buildings]] is measured at 50 Pa or 0.2 inches of water.<ref>{{cite web
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| |url = http://www.resnet.us/hotnews/revised_chapter_seven_final_9-16-10.pdf
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| |title = Chapter 7 ResNet Standards: ResNet National Standard for Home Energy Audits
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| |publisher=[[ResNet]]
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| |year = 2010
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| |accessdate =3 March 2011}}</ref>
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| ===Hectopascal and millibar units===
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| {{main|Bar (unit)}}
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| [[Meteorologists]] worldwide have for a long time measured atmospheric pressure in [[Bar (unit)|bars]], which was originally equivalent to the average air pressure on Earth; the bar was divided into a thousand millibars to provide the precision meteorologists require. After the introduction of [[SI units]], many preferred to preserve the customary pressure figures. Consequently, the bar was redefined as 100,000 pascals, which is only slightly lower than standard air pressure on Earth. Today many meteorologists prefer hectopascals (hPa) for air pressure, which are equivalent to millibars, while similar pressures are given in kilopascals in practically all other fields, since the [[Hecto-|hecto]] prefix is rarely used. Since official [[metrication]], meteorologists in Canada use kilopascals (kPa),<ref>[http://www.ctv.ca/servlet/HTMLTemplate/!ctvDynNews/Weather/Weather?City=Montreal CTV News, weather; current conditions in Montreal]</ref><ref>[http://www.weatheroffice.gc.ca/city/pages/qc-147_metric_e.html Environment Canada weather, current conditions in Montreal]</ref> although in some other countries hectopascals are still in use.<ref>[http://www.knmi.nl/actueel/ KNMI]</ref><ref>[http://www.kmi.be/nederlands/index.php?menu=Menu1_3 KMI]</ref><ref>[http://www.dwd.de/de/WundK/W_aktuell/Beobachtungen.htm DWD]</ref><ref>[http://www.jma.go.jp/en/g3/index.html JMA]</ref><ref>[http://www.meteoam.it/modules.php?name=analisiPrevisioniSuolo MDD]</ref><ref>[http://weather.noaa.gov/weather/current/KDCA.html NOAA]</ref><ref>[http://www.metoffice.gov.uk/guide/weather/symbols#units UK Met Office]</ref>
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| As of 17 November 2011 the hectopascal is used in aviation as the altimeter setting.
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| :1 hectopascal (hPa) ≡ 100 Pa ≡ 1 mbar.
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| :1 kilopascal (kPa) ≡ 1000 Pa ≡ 10 hPa ≡ 10 mbar.
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| == See also ==
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| * [[Orders of magnitude (pressure)]]
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| * [[Pascal's law]]
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| == Notes and references ==
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| {{Reflist|2}}
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| {{SI units}}
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| [[Category:SI derived units]]
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| [[Category:Units of pressure]]
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| [[Category:Blaise Pascal]]
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