Pascal (unit)
pascal | |
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![]() Apressure gaugereading inpsi(red scale) and kPa (black scale) | |
General information | |
Unit system | SI |
Unit of | pressureorstress |
Symbol | Pa |
Named after | Blaise Pascal |
Conversions | |
1 Pain... | ... is equal to... |
SI base units: | kg⋅m−1⋅s−2 |
US customary units: | 1.45038×10−4psi |
atmosphere: | 9.86923×10−6atm |
bar: | 10−5bar |
barye(CGS unit) | 10 Ba |
Thepascal(symbol:Pa) is the unit ofpressurein theInternational System of Units (SI).It is also used to quantifyinternal pressure,stress,Young's modulus,andultimate tensile strength.The unit, named afterBlaise Pascal,is anSI coherent derived unitdefined as onenewtonpersquare metre(N/m2).[1]It is also equivalent to 10barye(10 Ba) in theCGSsystem. Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa), which is equal to onemillibar,and the kilopascal (1 kPa = 1000 Pa), which is equal to one centibar.
The unit of measurement calledstandard atmosphere (atm)is defined as 101,325 Pa.[2] Meteorologicalobservations typically reportatmospheric pressurein hectopascals per the recommendation of theWorld Meteorological Organization,thus a standard atmosphere (atm) or typical sea-level air pressure is about 1013 hPa. Reports in the United States typically useinches of mercury[3]or millibars (hectopascals).[4][5]In Canada these reports are given in kilopascals.[6]
Etymology
[edit]The unit is named afterBlaise Pascal,noted for his contributions to hydrodynamics and hydrostatics, and experiments with abarometer.The namepascalwas adopted for the SI unit newton per square metre (N/m2) by the 14thGeneral Conference on Weights and Measuresin 1971.[7][8]
Definition
[edit]The pascal can be expressed usingSI derived units,or alternatively solelySI base units,as:
where N is thenewton,m is themetre,kg is thekilogram,s is thesecond,and J is thejoule.[9]
One pascal is the pressure exerted by a force of magnitude one newton perpendicularly upon an area of one square metre.
Standard units
[edit]The unit of measurement called anatmosphere or a standard atmosphere(atm) is101325Pa (101.325 kPa).[10]This value is often used as a reference pressure and specified as such in some national and international standards, such as theInternational Organization for Standardization's ISO 2787 (pneumatic tools and compressors),ISO 2533(aerospace) and ISO 5024 (petroleum). In contrast,International Union of Pure and Applied Chemistry(IUPAC) recommends the use of 100 kPa as a standard pressure when reporting the properties of substances.[11]
Unicodehas dedicated code-pointsU+33A9㎩SQUARE PAandU+33AA㎪SQUARE KPAin theCJK Compatibilityblock, but these exist only for backward-compatibility with some older ideographic character-sets and are thereforedeprecated.[12][13]
Uses
[edit]The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced thepounds per square inch(psi) unit, except in some countries that still use theimperial measurement systemor theUS customary system,including the United States.
Geophysicistsuse the gigapascal (GPa) in measuring or calculating tectonic stresses and pressures within theEarth.
Medicalelastographymeasures tissue stiffness non-invasively withultrasoundormagnetic resonance imaging,and often displays theYoung's modulusorshear modulusof tissue in kilopascals.
Inmaterials scienceandengineering,the pascal measures thestiffness,tensile strengthandcompressive strengthof materials. In engineering the megapascal (MPa) is the preferred unit for these uses, because the pascal represents a very small quantity.
Material | Young's modulus (GPa) |
---|---|
Nylon 6 | 2–4 |
Hempfibre | 35 |
Aluminium | 69 |
Tooth enamel | 83 |
Copper | 117 |
Structuralsteel | 200 |
Diamond | 1220 |
The pascal is also equivalent to the SI unit ofenergy density,the joule per cubic metre. This applies not only to the thermodynamics of pressurised gases, but also to the energy density ofelectric,magnetic,andgravitationalfields.
The pascal is used to measuresound pressure.Loudnessis the subjective experience of sound pressure and is measured as asound 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 thethreshold of hearingfor humans and is a common reference pressure, so that its SPL is zero.
The airtightness of buildingsis measured at 50 Pa.[15]
In medicine, blood pressure is measured inmillimeters of mercury(mmHg, very close to oneTorr). The normal adult blood pressure is less than 120 mmHg systolic BP (SBP) and less than 80 mmHg diastolic BP (DBP).[16]Convert mmHg to SI units as follows:1 mmHg = 0.13332 kPa.Hence normal blood pressure in SI units is less than 16.0 kPa SBP and less than 10.7 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
[edit]The units of atmospheric pressure commonly used inmeteorologywere formerly thebar(100,000 Pa), which is close to the average air pressure on Earth, and the millibar. Since the introduction ofSI units,meteorologists generally measure pressures in hectopascals (hPa) unit, equal to 100 pascals or 1 millibar.[17][18][19][20][21][22][23]Exceptions include Canada, which uses kilopascals (kPa). In many other fields of science, prefixes that are a power of 1000 are preferred, which excludes the hectopascal from use.[24][25]
Many countries also use millibars. In practically all other fields, the kilopascal is used instead.[26]
Multiples and submultiples
[edit]Decimal multiples and submultiples are formed using standardSI units.
Multiples | Submultiples | ||||
---|---|---|---|---|---|
Value | Name | Symbol | Value | Name | Symbol |
101Pa | decapascal | daPa | 10−1Pa | decipascal | dPa |
102Pa | hectopascal | hPa | 10−2Pa | centipascal | cPa |
103Pa | kilopascal | kPa | 10−3Pa | millipascal | mPa |
105Pa | bar (non-SI unit) | bar | |||
106Pa | megapascal | MPa | 10−6Pa | micropascal | μPa |
109Pa | gigapascal | GPa | 10−9Pa | nanopascal | nPa |
1012Pa | terapascal | TPa | 10−12Pa | picopascal | pPa |
1015Pa | petapascal | PPa | 10−15Pa | femtopascal | fPa |
1018Pa | exapascal | EPa | 10−18Pa | attopascal | aPa |
1021Pa | zettapascal | ZPa | 10−21Pa | zeptopascal | zPa |
1024Pa | yottapascal | YPa | 10−24Pa | yoctopascal | yPa |
1027Pa | ronnapascal | RPa | 10−27Pa | rontopascal | rPa |
1030Pa | quettapascal | QPa | 10−30Pa | quectopascal | qPa |
See also
[edit]- Atmospheric pressurewhich gives the usage of the hbar and the mbar
- Centimetre of water
- Meteorology
- Metric prefix
- Orders of magnitude (pressure)
- Pascal's law
- Pressure measurement
References
[edit]- ^International Bureau of Weights and Measures(2006),The International System of Units (SI)(PDF)(8th ed.), p. 118,ISBN92-822-2213-6,archived(PDF)from the original on 4 June 2021,retrieved16 December2021
- ^"Definition of the standard atmosphere".BIPM.Retrieved16 February2015.
- ^"National Weather Service glossary page on inches of mercury".
- ^"US government atmospheric pressure map".
- ^"The Weather Channel".
- ^Canada, Environment (16 April 2013)."Canadian Weather - Environment Canada".weather.gc.ca.
- ^bipm.fr.Archived30 June 2007 at theWayback Machine.
- ^Minutes of the 14. General Conference on Weights and Measures,1971, p. 78.
- ^Table 3 (Section 2.2.2).Archived18 June 2007 at theWayback Machine.SI Brochure.International Bureau of Weights and Measures.
- ^"Resolution 4 of the 10th meeting of the CGPM".Conférence Générale des Poids et Mesures.1954. Archived fromthe originalon 30 March 2021.Retrieved5 April2010.
- ^IUPAC.org, Gold Book,Standard Pressure
- ^"CJK Compatibility"(PDF).2015.Retrieved21 February2016.
- ^The Unicode Standard, Version 8.0.0.Mountain View, CA: The Unicode Consortium. 2015.ISBN978-1-936213-10-8.Retrieved21 February2016.
- ^"Tensile Modulus – Modulus of Elasticity or Young's Modulus – for some common Materials".Retrieved16 February2015.
- ^"Chapter 7 ResNet Standards: ResNet National Standard for Home Energy Audits"(PDF).ResNet. 2010. Archived fromthe original(PDF)on 26 July 2011.Retrieved3 March2011.
- ^"BP Guideline | Target:BP".American Heart Association.Retrieved18 May2020.
- ^"KNMI – Weer – Waarnemingen".Retrieved4 December2016.
- ^"Comment convertir la pression? – IRM".Retrieved4 December2016.
- ^"DWD".Archived fromthe originalon 10 February 2008.Retrieved20 December2006.
- ^"Japan Meteorological Agency – Weather Maps".Retrieved4 December2016.
- ^"MDD".Archived fromthe originalon 6 May 2006.
- ^NOAA
- ^United Kingdom, Met Office."Key to symbols and terms".Retrieved4 December2016.
- ^"CTV News, weather; current conditions in Montreal".Archived fromthe originalon 4 June 2011.
- ^Canada, Environment."Montréal, QC – 7 Day Forecast – Environment Canada".Archived fromthe originalon 30 November 2017.Retrieved4 December2016.
- ^Ambler Thompson (Editor)Guide for the Use of the International System of Units (SI) (rev. ): The...,p. 66, atGoogle Books