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Information about Pascal (unit)

The pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Young's modulus and tensile strength). It is a measure of perpendicular force per unit area i.e. equivalent to one newton per square meter or one Joule per cubic meter. In everyday life, the pascal is perhaps best known from meteorological air-pressure reports, where it occurs in the form of hectopascal (1 hPa = 100 Pa).[1] In other contexts, the kilopascal is more commonly used, for example on bicycle tire labels[2]. One hectopascal corresponds to about 0.1% and one kilopascal to about 1% of atmospheric pressure (near sea level).

Definition

1 pascal (Pa) ≡ 1 N·m−2 ≡ 1 J·m−3 ≡ 1 kg·m−1·s−2


Pressure Units
 
pascal
(Pa)
bar
(bar)		 technical atmosphere
(at)
atmosphere
(atm)
torr
(mmHg)		 pound-force per
square inch
(psi)
1 Pa≡ 1 N/m210−51.019710−59.869210−67.500610−3145.0410−6
1 bar100 000≡ 106 dyn/cm21.01970.98692750.0614.504
1 at98 066.50.980665≡ 1 kgf/cm20.96784735.5614.223
1 atm101 3251.013251.0332≡ 1 atm76014.696
1 torr133.3221.333210−31.359510−31.315810−3≡ 1 mmHg19.33710−3
1 psi6 894.7668.94810−370.30710−368.04610−351.715≡ 1 lbf/in2
Example reading:  1 Pa = 1 N/m2  = 10−5 bar  = 10.19710−6 at  = 9.869210−6 atm, etc.
Note:  mmHg is an abbreviation for millimetres of mercury.

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. [1]

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.

Miscellany

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).[3]

The Unicode computer character set has dedicated symbols ㎩ (U+33A9) for Pa and ㎪ (U+33AA) 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 (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 Montréal and CBC weather, current conditions in Montréal, 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.


In the former mts system, the unit of pressure is the pièze (symbol pz), which is equal to one kilopascal.

In the former cgs system, the unit of pressure is the barye (symbol ba), which is equal to one decipascal.

Vehicle owners' guides now specify tire inflation in kilopascals.

See also

References

1. ^ World Meteorological Organization: Manual on the Global Observing System – Volume I, Section 3.3.2.2: "The hectopascal (hPa), equal to 100 pascals (Pa), shall be the unit in which pressures are reported for meteorological purposes."
2. ^ ISO 5775: Bicycle tyres and rims
3. ^ http://www.compressor.co.za/news/may%20news.htm.

Further reading

SI derived units are part of the SI system of measurement units and are derived from the seven SI base units.

Dimensionless derived units

The following SI units are actually dimensionless ratios, formed by dividing two identical SI units.
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Pressure (symbol: p) is the force per unit area applied on a surface in a direction perpendicular to that surface.

Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.
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Stress is a measure of force per unit area within a body. It is a body's internal distribution of force per area that reacts to external applied loads. Stress is often broken down into its shear and normal components as these have unique physical significance.
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Young's modulus (E) is a measure of the stiffness of a given material. It is also known as the Young modulus, modulus of elasticity, elastic modulus or tensile modulus (the bulk modulus and shear modulus are different types of elastic modulus).
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Tensile strength , or measures the force required to pull something such as rope, wire, or a structural beam to the point where it breaks.

Explanation


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In physics, force is an action or agency that causes a body of mass m to accelerate. It may be experienced as a lift, a push, or a pull. The acceleration of the body is proportional to the vector sum of all forces acting on it (known as net force or resultant force).
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Area is a physical quantity expressing the size of a part of a surface. The term Surface area is the summation of the areas of the exposed sides of an object.

Units

Units for measuring surface area include:
square metre = SI derived unit

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The newton (symbol: N) is the SI derived unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics.

Definition

A newton
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square metre (also spelled meter, see spelling differences) is the SI derived unit of area, with symbol m². It is defined as the area of a square whose sides measure exactly one metre.
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Atmospheric pressure is the pressure at any point in the Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point.
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The newton (symbol: N) is the SI derived unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics.

Definition

A newton
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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The joule (IPA: [dʒuːl] or [dʒaʊl]) (symbol: J) is the SI unit of energy.
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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kilogram or kilogramme (symbol: kg) is the SI base unit of mass. The kilogram is defined as being equal to the mass of the International Prototype Kilogram (IPK), which is almost exactly equal to the mass of one liter of water.
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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second (SI symbol: s), sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units (SI) base unit of time.

SI prefixes are frequently combined with the word second to denote subdivisions of the second, e.g.
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The bar (symbol bar), decibar (symbol dbar) and the millibar (symbol mbar, also mb) are units of pressure. They are not SI units, but they are accepted for use with the SI.
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A technical atmosphere (symbol: at) is a non-SI unit of pressure equal to 1 kilogram-force per square centimeter, i.e. 98.0665 kilopascals (kPa) or about 0.967 84 standard atmospheres.
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Standard atmosphere is a pressure defined as 101 325 Pa and used as unit of pressure (symbol: atm). Standard atmosphere is a non-SI unit that is internationally recognized.
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torr (symbol: Torr) is a non-SI unit of pressure defined as 1/760 of an atmosphere. It was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644.
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pound per square inch or, more accurately, pound-force per square inch (symbol: psi or lbf/sq in) is a unit of pressure or of stress based on avoirdupois units.
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The newton (symbol: N) is the SI derived unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics.

Definition

A newton
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Dynes redirects here. For the president of the University of California system, see Robert C. Dynes.


In physics, the dyne (symbol "dyn") is a unit of force specified in the centimeter-gram-second
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The unit kilogram-force (kgf, often just kg) or kilopond (kp) is defined as the force exerted by one kilogram of mass in standard Earth gravity.
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Standard atmosphere is a pressure defined as 101 325 Pa and used as unit of pressure (symbol: atm). Standard atmosphere is a non-SI unit that is internationally recognized.
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torr (symbol: Torr) is a non-SI unit of pressure defined as 1/760 of an atmosphere. It was named after Evangelista Torricelli, an Italian physicist and mathematician who discovered the principle of the barometer in 1644.
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A pound or pound-force (abbreviations: lb, lbf, or lbf) is a unit of force. Pound is also the name of a unit of mass. One pound-force is approximately equal to the gravitational force exerted on a mass of one avoirdupois pound on the
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Blaise Pascal (pronounced [blɛːz paskal]), (June 19 1623 – August 19 1662) was a French mathematician, physicist, and religious philosopher. He was a child prodigy who was educated by his father.
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Motto
Liberté, Égalité, Fraternité
"Liberty, Equality, Fraternity"
Anthem
"La Marseillaise"


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