The pascal (symbol: Pa) is the
Contents 1 Etymology 2 Definition 3 Standard units 4 Uses 4.1 Hectopascal and millibar units 5 See also 6 References 7 External links Etymology[edit]
The unit is named after Blaise Pascal, noted for his contributions to
hydrodynamics and hydrostatics, and experiments with a barometer. The
name pascal was adopted for the SI unit newton per square metre (N/m2)
by the 14th
1 P a = 1 N m 2 = 1 k g m ⋅ s 2 = J m 3 displaystyle rm 1~Pa=1~ frac N m^ 2 =1~ frac kg mcdot s^ 2 = frac J m^ 3 where N is the newton, m is the metre, kg is the kilogram, s is the
second, and J is the joule.[4]
One pascal is the pressure exerted by a force of magnitude one newton
perpendicularly upon an area of one square metre.
Standard units[edit]
The unit of measurement called an atmosphere or a standard atmosphere
(atm) is 101325 Pa (101.325 kPa).[5] This value is often
used as a reference pressure and specified as such in some national
and international standards, such as the International Organization
for Standardization's ISO 2787 (pneumatic tools and compressors),
ISO 2533 (aerospace) and ISO 5024 (petroleum). In contrast,
This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2016) (Learn how and when to remove this template message) 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 or the US customary system,
including the United States.
Geophysicists use the gigapascal (GPa) in measuring or calculating
tectonic stresses and pressures within the Earth.
Medical elastography measures tissue stiffness non-invasively with
ultrasound or magnetic resonance imaging, and often displays the
Approximate
Material Young's modulus nylon 6 2–4 GPa hemp fibre 35 GPa aluminium 69 GPa tooth enamel 83 GPa copper 117 GPa structural steel 200 GPa diamond 1220 GPa The pascal is also equivalent to the SI unit of energy density, J/m3. This applies not only to the thermodynamics of pressurised gases, but also to the energy density of electric, magnetic, and gravitational fields. In measurements of sound pressure or loudness of sound, one pascal is equal to 94 decibels SPL. The quietest sound a human can hear, known as the threshold of hearing, is 0 dB SPL, or 20 µPa. The airtightness of buildings is measured at 50 Pa.[10] Hectopascal and millibar units[edit] Main article: Bar (unit) 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.[11][12][13][14][15][16][17] Exceptions include Canada, which use kilopascals (kPa). In many other fields of science, the SI is preferred, which means Pa with a prefix (in multiples of 1000) is preferred.[18][19] Many countries also use the millibars. In practically all other fields, the kilopascal (1000 pascals) is used instead.[citation needed] See also[edit] Centimetre of water Metric prefix Orders of magnitude (pressure) Pascal's law References[edit] ^
External links[edit] v t e SI units Authority:
Base units ampere candela kelvin kilogram metre mole second Derived units with special names becquerel coulomb degree Celsius farad gray henry hertz joule katal lumen lux newton ohm pascal radian siemens sievert steradian tesla volt watt weber Other accepted units astronomical unit bar dalton day decibel degree of arc electronvolt hectare hour litre minute minute of arc neper second of arc tonne atomic units natural units See also Conversion of units Metric prefixes Proposed redefinitions Systems of measurement |