Pascal
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The pascal (symbol: Pa) is the SI unit of pressure. It is equivalent to one newton per square meter, and was used in SI under that name before the name pascal was adopted by the 14th CGPM in 1971. The same unit is also used for stress, Young's modulus, and tensile strength.
Definition
1 pascal (Pa) = 1 N/m2 = 1 J/m3 = 1 kg·m–1·s–2
Origin
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.
Explanation
1 megapascal (MPa) = 1 000 000 Pa = 1 N/mm2.
Standard atmospheric pressure is 101 325 Pa = 101.325 kPa = 1013.25 hPa = 1013.25 mbar = 760 Torr. This definition is used for pneumatic fluid power (ISO R554), and in the aerospace (ISO 2533) and petroleum (ISO 5024) industries.
In 1985, IUPAC recommended that standard atmospheric pressure should be harmonized to 100 000 Pa = 1 bar = 750 Torr. The same definition is used in the compressor and the pneumatic tool industries (ISO 2787). [link]
The Unicode computer character set has dedicated symbols ㎩ (U+{{{1) for Pa and ㎪ (U+{{{1) for kPa, but these exist merely for backward-compatibility with some older ideographic character-sets and are therefore deprecated.
Uses
Meteorologists worldwide have for a long time measured atmospheric pressure in millibars. After the introduction of SI units, many preferred to preserve the customary pressure figures. Therefore, meteorologists use hectopascals today for air pressure, which are equivalent to millibars, while similar pressures are given in kilopascals in practically all other fields, where the hecto prefix is hardly ever used.
- 1 hectopascal (hPa) = 100 Pa = 1 mbar.
- 1 kilopascal (kPa) = 1000 Pa = 10 hPa.
Outside the US, vehicle owners' guides now specify tire inflation in kilopascals. The purchasing of foreign tires is the only place ordinary Americans will find this unit, and as the tire pumps in service stations are not calibrated in these units, they have to do the calculations to convert.
Comparison to other units of pressure
| 1 bar | 100 000 Pa |
| 1 barye | 0.1 Pa |
| 1 millibar | 100 Pa |
| 1 atmosphere | 101325 Pa |
| 1 mmHg (or Torr) | 133.322 Pa |
| 1 inHg | 3386.833 Pa |
| 1 cmH2O | 98.0638 Pa |
| Pascal (Pa) | Bar (bar) | Technical atmosphere (at) | Atmosphere (atm) | Torr (mmHg) | Pound per square inch (psi) | |
|---|---|---|---|---|---|---|
| 1 Pa | N/m² | 10−5 | ||||
| 1 bar | 100 000 | 6 dyne>dyn/cm² | 1.0197 | 0.98692 | 750.06 | 14.504 |
| 1 at | 98 066.5 | 0.980665 | kgf/cm² | 0.96784 | 735.56 | 14.223 |
| 1 atm | 101 325 | 1.01325 | 1.0332 | Pa | 760 | 14.696 |
| 1 Torr | 133.322 | mmHg | ||||
| 1 psi | 6,894.76 | 51.715 | lbf/in² |
Example reading: 1 Pa = 1 N/m² = 10−5 bar = 10.197×10−6 at = 9.8692×10−6 atm ....etc.
Note: mmHg is an abbreviation for millimetres of mercury.
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| This SI unit is named after Blaise Pascal. As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (Pa). But when an SI unit is spelled out, it should always be written in lowercase (pascal), unless it begins a sentence or is the name "degree Celsius". — Based on [The International System of Units], section 5.2.
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See also
External links
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