|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:||kg m-1 s-2|
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 of measurement called standard atmosphere (atm) is defined as 101.325 kPa and approximates to the average pressure at sea-level at 45° N. Meteorological reports typically state atmospheric pressure in hectopascals.
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.
The unit of measurement called atmosphere or standard atmosphere (atm) is 101325 Pa (101.325 kPa). This value is often used as a reference pressure and specified as such in some national and international standards, such as ISO 2787 (pneumatic tools and compressors), ISO 2533 (aerospace) and ISO 5024 (petroleum). In contrast, IUPAC recommends the use of 100 kPa as a standard pressure when reporting the properties of substances.
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.
In materials science and engineering, the pascal measures the stiffness, tensile strength and compressive strength of materials. In engineering use, because the pascal represents a very small quantity, the megapascal (MPa) is the preferred unit for these uses.
|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
The units of atmospheric pressure commonly used in meteorology were formerly the bar, which was close to the average air pressure on Earth, and the millibar. Since the introduction of SI units, meteorologists generally measure pressures in hectopascals (hPa) unit, equal to 100 pascals or 1 millibar. Exceptions include Canada and Portugal, which uses kilopascals (kPa). It should be noted that in many other fields of science, the SI is preferred, which means Pa with a prefix (in multiples of 3) is preferred.
Notes and references
- International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (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.
- IUPAC.org, Gold Book, Standard Pressure
- "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" (PDF). ResNet. 2010. Retrieved 3 March 2011.
- UK Met Office
- CTV News, weather; current conditions in Montreal
- Environment Canada weather, current conditions in Montreal