Pascal (unit)
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| Pascal (unit) | |
|---|---|
| Name | Pascal |
| Standard | SI |
| Quantity | Pressure, Stress |
| Namedafter | Blaise Pascal |
| Units1 | SI base units |
| Inunits1 | kg⋅m−1⋅s−2 |
| Units2 | Atmosphere |
| Inunits2 | ≈ 9.8692×10−6 atm |
| Units3 | Bar |
| Inunits3 | 10−5 bar |
| Units4 | Pound per square inch |
| Inunits4 | ≈ 1.4504×10−4 psi |
Pascal (unit). The pascal, symbolized as Pa, is the SI derived unit of pressure and stress. It is defined as one newton of force applied per one square metre of area, establishing a fundamental relationship between force, area, and distributed load. Named in honor of the French polymath Blaise Pascal, the unit was formally adopted into the modern metric system in 1971 by the General Conference on Weights and Measures.
Definition and equivalence
The pascal is defined as the pressure exerted by a force of one newton acting uniformly over an area of one square metre. This derives directly from its expression in SI base units as one kilogram per metre per second squared. Consequently, one pascal is equivalent to one joule per cubic metre, linking it directly to concepts of energy density in thermodynamics. This definition provides a coherent and scalable framework for measuring atmospheric pressure, fluid pressures, and material stresses across scientific and engineering disciplines.
SI multiples and common usage
Due to its relatively small magnitude, the pascal is often used with SI prefixes to describe practical pressures. For instance, hectopascals are the standard unit in meteorology for reporting barometric pressure, where one standard atmosphere is approximately 1013.25 hPa. In material science and engineering, megapascals and gigapascals are commonly used to express the tensile strength of steel or the bulk modulus of diamond. Conversely, very low pressures, such as those in vacuum systems, may be reported in millipascals.
History and adoption
The unit was named for Blaise Pascal, the renowned 17th-century French mathematician, physicist, and philosopher whose work, including experiments with barometers and foundational contributions to fluid mechanics and hydrostatics, laid the groundwork for the modern understanding of pressure. The pascal was officially incorporated into the SI at the 14th CGPM in 1971, replacing earlier metric units like the barye and the technical atmosphere. This adoption was part of a broader effort to standardize coherent derived units and simplify international scientific communication.
Practical examples and context
To contextualize its magnitude, standard atmospheric pressure at sea level is about 101,325 pascals, while the pressure under the tire of a typical car might be around 200,000 Pa. In medicine, blood pressure is traditionally measured in millimetres of mercury, with 120 mmHg systolic pressure equating to roughly 16,000 Pa. The immense pressures in geological contexts, such as at the bottom of the Mariana Trench, can exceed 100 megapascals, and those within the Earth's core reach into the terapascal range.
Related units and conversions
The pascal is part of a family of pressure units with historical or specialized use. The bar, equal to 100,000 pascals, is widely used in geophysics and oceanography. The pound per square inch remains common in the United States and the United Kingdom, especially for tire pressure and scuba diving tanks. Other non-SI units include the torr, nearly identical to the mmHg, and the atmosphere, defined as 101,325 Pa exactly. Precise conversion between these units is essential in fields like aerospace engineering and process engineering.
Category:SI derived units Category:Units of pressure