The
pascal (symbol:
Pa) is the
SI derived unit of
pressure,
stress,
Young's modulus and
tensile strength. It is a measure of
force per unit
area,
defined as one
newton per
square metre. In everyday life, the pascal is
perhaps best known from meteorological
barometric pressure reports, where it
occurs in the form of hectopascals(1 hPa ≡ 100 Pa) or
kilopascals (1 kPa = 1000 Pa). In other contexts, the
kilopascal is commonly used, for example on
bicycle tire labels. One hectopascal
corresponds to about 0.1% and one kilopascal to about 1% of
atmospheric pressure (near sea
level). One hectopascal is equivalent to one
millibar; one
atmosphere is exactly equal to 1013.25
hPa.
Definition
- 1 pascal (Pa) = 1 N/m^{2} =
1 kg/(m·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.The name
pascal was adopted for the SI unit
newton per
square
metre by the 14th
CGPM in 1971.
[10351]
Miscellaneous
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).
The
Unicode computer character set has
dedicated symbols ( ) for Pa and ( ) for kPa, but these exist
merely for backward-compatibility with some older ideographic
character-sets and are therefore
deprecated.
Uses
The pascal (Pa) or kilopascal (kPa) as a unit of pressure
measurement is widely used throughout the world and largely
replaces the pounds per square inch (psi) unit except in some
countries still using the
Imperial measurement
system.
Tectonophysicists use the gigapascal
(GPa) in measuring or calculating tectonic forces within the
earth.
Another unit for pressure measurement in common use today is
millimetres of water (1 mm H
_{2}O = 9.80665 Pa).
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 (hPa)
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. Since official
metrication, meteorologists in Canada
use kilopascals (kPa), see for example
CTV News, weather; current conditions in
Montreal and
CBC weather, current conditions in Montreal, although
in some other countries hectopascals are still in use, see for
example
KNMI,
KMI,
DWD,
JMA,
MDD and
NOAA.
- 1 hectopascal (hPa) ≡ 100 Pa ≡ 1 mbar.
- 1 kilopascal (kPa) ≡ 1000 Pa ≡ 10 hPa ≡
10 mbar.
In the
cgs
system, the unit of pressure is the
barye
(symbol
ba), which is equal to one
decipascal.
In the former
mts
system, the unit of pressure is the
pièze (symbol
pz), which is
equal to one kilopascal.
Vehicle owners' guides now specify
tire
inflation in kilopascals.
Airtightness testing of buildings is
measured at 50 Pa or 0.2 inches of water.
See also
References
- U.S. Federal Meteorological Handbook
- ISO 5775: Bicycle
tires and rims
- Table 3 (Section 2.2.2), SI Brochure,
International
Bureau of Weights and Measures