Editing Pascal (unit) (section)

== Uses ==
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]] or the [[US customary system]], including the United States.

[[Geophysics|Geophysicists]] use the gigapascal (GPa) in measuring or calculating tectonic stresses and pressures within the [[Earth]].

Medical [[elastography]] measures tissue stiffness non-invasively with [[medical ultrasonography|ultrasound]] or [[magnetic resonance imaging]], and often displays the [[Young's modulus]] or [[shear modulus]] of tissue in kilopascals.

In [[materials science]] and [[engineering]], the pascal measures the [[Young's modulus|stiffness]], [[tensile strength]] and [[compressive strength]] of materials. In engineering the megapascal (MPa) is the preferred unit for these uses, because the pascal represents a very small quantity.

{| class="wikitable"
|+ Approximate Young's modulus for common substances<ref>{{cite web|url=http://www.engineeringtoolbox.com/young-modulus-d_417.html|title=Tensile Modulus – Modulus of Elasticity or Young's Modulus – for some common Materials|access-date=2015-02-16}}</ref>
! Material !! Young's modulus {{br}}(GPa)
|-
| [[Nylon 6]] ||align="right"| 2–4 
|-
| [[Hemp]] fibre ||align="right"| 35 
|-
| [[Aluminium]] ||align="right"| 69 
|-
| [[Tooth enamel]] ||align="right"| 83 
|-
| [[Copper]] ||align="right"| 117 
|-
| Structural [[steel]] ||align="right"| 200 
|-
| [[Diamond]] ||align="right"| 1220 
|}

The pascal is also equivalent to the SI unit of [[energy density]], the joule per cubic metre. This applies not only to the thermodynamics of pressurised gases, but also to the energy density of [[electric potential energy|electric]], [[magnetic field#Energy stored in magnetic fields|magnetic]], and [[gravitational energy|gravitational]] fields.

The pascal is used to measure [[sound pressure]]. [[Loudness]] is the subjective experience of sound pressure and is measured as a [[Sound pressure#Sound pressure level|sound pressure level]] (SPL) on a logarithmic scale of the sound pressure relative to some reference pressure. For sound in air, a pressure of 20 μPa is considered to be at the [[threshold of hearing]] for humans and is a common reference pressure, so that its SPL is zero.

[[Blower door|The airtightness of buildings]] is measured at 50&nbsp;Pa.<ref>
{{cite web
 |url         = http://www.resnet.us/hotnews/revised_chapter_seven_final_9-16-10.pdf
 |title       = Chapter 7 ResNet Standards: ResNet National Standard for Home Energy Audits
 |publisher   = ResNet
 |year        = 2010
 |access-date  = 2011-03-03
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110726045004/http://www.resnet.us/hotnews/revised_chapter_seven_final_9-16-10.pdf
 |archive-date = 26 July 2011
}}</ref>

In medicine, blood pressure is measured in [[Millimetre of mercury|millimeters of mercury]] (mmHg, very close to one [[Torr]]).  The normal adult blood pressure is less than 120&nbsp;mmHg systolic BP (SBP) and less than 80&nbsp;mmHg diastolic BP (DBP).<ref>{{cite web |title=BP Guideline {{!}} Target:BP |url=https://targetbp.org/guidelines17/ |website=American Heart Association |access-date=18 May 2020}}</ref> Convert mmHg to SI units as follows: {{nowrap|1= 1 mmHg = {{val|0.13332|u=kPa}}}}. Hence the normal blood pressure in SI units is less than 16.0&nbsp;kPa SBP and less than 10.7&nbsp;kPa DBP. These values are similar to the pressure of water column of average human height; so pressure has to be measured on arm roughly at the level of the heart.

=== Hectopascal and millibar units ===
{{main|Bar (unit)}}
The units of atmospheric pressure commonly used in [[meteorology]] were formerly the [[Bar (unit)|bar]] ({{val|100,000|u=Pa}}), which is close to the average air pressure on Earth, and the millibar. Since the introduction of [[International System of Units|SI units]], meteorologists generally measure atmospheric pressure in hectopascals (hPa), equal to 100 pascals or 1 millibar.<ref>{{cite web|url=http://www.knmi.nl/actueel/|title=KNMI – Weer – Waarnemingen|access-date=4 December 2016}}</ref><ref>{{cite web|url=http://www.meteo.be/meteo/view/fr/68771-FAQ%20sur%20le%20temps.html?view=195695|title=Comment convertir la pression? – IRM|access-date=4 December 2016}}</ref><ref>{{Cite web|url=http://www.dwd.de/de/WundK/W_aktuell/Beobachtungen.htm|title=DWD|access-date=20 December 2006|archive-url=https://web.archive.org/web/20080210040845/http://www.dwd.de/de/WundK/W_aktuell/Beobachtungen.htm|archive-date=10 February 2008|url-status=dead}}</ref><ref>{{cite web|url=http://www.jma.go.jp/en/g3/index.html|title=Japan Meteorological Agency – Weather Maps|access-date=4 December 2016}}</ref><ref>{{Cite web|url=http://www.meteoam.it/modules.php?name=analisiPrevisioniSuolo|archive-url=https://web.archive.org/web/20060506192242/http://www.meteoam.it/modules.php?name=analisiPrevisioniSuolo|url-status=dead|title=MDD|archive-date=6 May 2006}}</ref><ref>[http://weather.noaa.gov/weather/current/KDCA.html NOAA]</ref><ref>{{cite web|url=http://www.metoffice.gov.uk/guide/weather/symbols#units|title=Key to symbols and terms|first=Met Office|last=United Kingdom|access-date=4 December 2016}}</ref> Exceptions include Canada, which uses kilopascals (kPa). In many other fields of science, prefixes that are a power of 1000 are preferred, which theoretically excludes hectopascal from use.<ref>{{Cite web|url=http://www.ctv.ca/servlet/HTMLTemplate/!ctvDynNews/Weather/Weather?City=Montreal|archive-url=https://web.archive.org/web/20110604131321/http://www.ctv.ca/servlet/HTMLTemplate/!ctvDynNews/Weather/Weather?City=Montreal|url-status=dead|title=CTV News, weather; current conditions in Montreal|archive-date=4 June 2011}}</ref><ref>{{cite web|url=http://www.weatheroffice.gc.ca/city/pages/qc-147_metric_e.html|title=Montréal, QC – 7 Day Forecast – Environment Canada|first=Environment|last=Canada|access-date=4 December 2016|archive-date=30 November 2017|archive-url=https://web.archive.org/web/20171130163853/http://www.weatheroffice.gc.ca/city/pages/qc-147_metric_e.html|url-status=dead}}</ref>

Many countries still use millibars to measure atmospheric pressure. In practically all other fields, the kilopascal is used instead.<ref>Ambler Thompson (Editor) {{google books|pTw-SCI7EkoC|Guide for the Use of the International System of Units (SI) (rev. ): The ...|page=66}}</ref>