Pascal

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The pascal (symbol Pa) is the SI unit of pressure. It is equivalent to one newton per square metre. The unit is named after Blaise Pascal, the eminent French mathematician, physicist and philosopher.

1 Pa: = 1 N/m² = 1 (kg·m/s²)/m² = 1 kg/m·s²; = 0.01 millibar; = 0.00001 bar

The same unit is also used for stress, Young's modulus and tensile strength.

Standard atmospheric pressure is 101 325 Pa = 101.325 kPa = 1013.25 hPa = 1013.25 mbar = 760 Torr (ISO 2533).

Meteorologists world-wide have for a long time measured air 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

In the former Soviet mts system the unit of pressure is the pieze, which is equivalent to one kilopascal.

The Unicode computer character set has dedicated symbols ㎩ for Pa and ㎪ for kPa, but these exist merely for backwards-compatibility with some older ideographic character sets.

Examples of various values (approximately)

(See SI prefix for guide to units.)

0.5 Pa	Atmospheric pressure on Pluto (1988 figure; very roughly)
10 Pa	Pressure increase per 1 mm of a water column¹
1 kPa	Atmospheric pressure on Mars, ∼1 % of atmospheric sea-level pressure on Earth
10 kPa	Pressure increase per 1 m of a water column¹, or the drop in air pressure when going from Earth sea level to 1000 m elevation
101.325 kPa	Standard atmospheric pressure for Earth sea level = 1013.25 hPa
10 MPa	Pressure washers force out water at this pressure
100 MPa	Pressure at bottom of Mariana Trench, about 10 km below ocean surface
10 GPa	Diamond forms
100 GPa	Theoretical tensile strength of carbon nanotubes (CNTs)

¹at the Earth's surface

Comparison to other units of pressure

1 bar	100 000 Pa
1 millibar	100 Pa
1 atmosphere	101 325 Pa
1 mmHg (or Torr)	133.332 Pa
1 inch Hg	3 386.833 Pa

Categories: SI derived units | Units of pressure

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01-04-2007 01:21:04

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