|This article needs additional citations for verification. (October 2011)|
|Unit system||SI derived unit|
|Unit of||Pressure or stress|
|Named after||Blaise Pascal|
|In SI base units:||1 Pa = 1 kg/(m·s2)|
The pascal (symbol: Pa) is the SI derived unit of pressure, internal pressure, stress, Young's modulus and ultimate tensile strength, defined as one newton per square metre. It is named after the French polymath Blaise Pascal.
Common multiple units of the pascal are the hectopascal (1 hPa ≡ 100 Pa) which is equal to 1 mbar, the kilopascal (1 kPa ≡ 1000 Pa), the megapascal (1 MPa ≡ 1,000,000 Pa), and the gigapascal (1 GPa ≡ 1,000,000,000 Pa).
The unit is named after Blaise Pascal, noted for his experiments with a barometer. The name pascal was adopted for the SI unit newton per square metre (N/m2) by the 14th General Conference on Weights and Measures in 1971.
In 1985 the IUPAC recommended that the standard for atmospheric pressure should be harmonized to 101325 Pa. The same definition is used in the compressor and the pneumatic tool industries (ISO 2787).
The Unicode computer character set has dedicated symbols ㎩ (U+33A9) for Pa and ㎪ (U+33AA) for kPa, but these exist merely for backward-compatibility with some older ideographic character-sets and are therefore deprecated.
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.
Geophysicists use the gigapascal (GPa) in measuring or calculating tectonic stresses and pressures within the Earth.
|nylon 6||2–4 GPa|
|hemp fibre||35 GPa|
|tooth enamel||83 GPa|
|structural steel||200 GPa|
The pascal is also equivalent to the SI unit of energy density, J/m3. This applies not only to the thermodynamics of pressurized gases, but also to the energy density of electric, magnetic, and gravitational fields.
Hectopascal and millibar units
Meteorologists worldwide have for a long time measured atmospheric pressure in bars, where one bar was originally equivalent to the average air pressure on Earth; the bar was divided into a thousand millibars to provide the granularity that 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 prefix is rarely used. Since official metrication, meteorologists in Canada use kilopascals (kPa), although in some other countries hectopascals are still in use.
As of 17 November 2011 the hectopascal is used in aviation as the altimeter setting.
- 1 hectopascal (hPa) ≡ 100 Pa ≡ 1 mbar.
- 1 kilopascal (kPa) ≡ 1000 Pa ≡ 10 hPa ≡ 10 mbar.
Notes and references
- International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), p. 118, ISBN 92-822-2213-6
- BIPM Definition of the standard atmosphere "Definition of the standard atmosphere". Retrieved 16 February 2015.
- U.S. Federal Meteorological Handbook
- Table 3 (Section 2.2.2), SI Brochure, International Bureau of Weights and Measures
- "Resolution 4 of the 10th meeting of the CGPM". Conférence Générale des Poids et Mesures (CGPM). 1954. Retrieved 5 April 2010.
- "Tensile Modulus - Modulus of Elasticity or Young's Modulus - for some common Materials". Retrieved 16 February 2015.
- "Chapter 7 ResNet Standards: ResNet National Standard for Home Energy Audits". ResNet. 2010. Retrieved 3 March 2011.
- CTV News, weather; current conditions in Montreal
- Environment Canada weather, current conditions in Montreal
- UK Met Office