The PASCAL (symbol: Pa) is the
Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa) which is equal to one millibar , and the kilopascal (1 kPa = 1000 Pa) which is equal to one centibar. The unit of measurement called standard atmosphere (atm) is defined as 101,325 Pa and approximates to the average pressure at sea-level at the latitude 45° N. Meteorological reports typically state atmospheric pressure in hectopascals. CONTENTS * 1 Etymology * 2 Definition * 3 Miscellaneous * 4 Uses * 4.1 Hectopascal and millibar units * 5 See also * 6 References * 7 External links ETYMOLOGY The unit is named after
DEFINITION The pascal can be expressed using SI derived units , or alternatively solely SI base units , as: 1 P a = 1 N m 2 = 1 k g m s 2 {displaystyle {rm {1~Pa=1~{frac {N}{m^{2}}}=1~{frac {kg}{mcdot s^{2}}}}}} where N is the newton , m is the metre , kg is the kilogram , and s is the second . One pascal is the pressure exerted by a force of magnitude one newton perpendicularly upon an area of one square metre. MISCELLANEOUS 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
USES 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
Geophysicists use the gigapascal (GPa) in measuring or calculating
tectonic stresses and pressures within the
Medical elastography measures tissue stiffness non-invasively with ultrasound or magnetic resonance imaging , and often displays the Young\'s modulus or shear modulus of tissue in kilopascals. 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. Approximate
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. HECTOPASCAL AND MILLIBAR UNITS Main article:
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 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. Many countries also use the millibar or hectopascal to give aviation altimeter settings . In practically all other fields, the kilopascal (1000 pascals) is used instead. SEE ALSO *
REFERENCES * ^
EXTERNAL |