pascal (unit)
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| pascal (unit) | |
|---|---|
| Name | pascal |
| Quantity | Pressure, stress |
| Standard | SI derived unit |
| Namedafter | Blaise Pascal |
| Abbr | Pa |
| Units1 | base SI units |
| Units1expr | N·m⁻2 = kg·m⁻1·s⁻2 |
pascal (unit) is the SI derived unit of pressure and stress, defined as one newton per square metre. It is used across physics, engineering, meteorology, and materials science to quantify force per unit area and mechanical stress in solids and fluids. The pascal is part of the International System of Units coordinated by bodies such as the Bureau International des Poids et Mesures, and it connects to a network of measurement standards employed by institutions worldwide.
Definition and SI context
The pascal is formally defined within the International System of Units as 1 Pa = 1 N·m⁻2, where the newton is the SI unit of force derived from the kilogram, metre, and second. Key organizations involved in the definition and dissemination of SI units include the Bureau International des Poids et Mesures, the International Committee for Weights and Measures, and national metrology institutes such as the National Institute of Standards and Technology, the National Physical Laboratory, and the Physikalisch-Technische Bundesanstalt. The pascal fits into the SI coherence that links base units—kilogram, metre, second—to derived quantities like pressure and energy density used in standards from the International Organization for Standardization to the World Meteorological Organization.
History and etymology
The unit is named after Blaise Pascal, a 17th-century mathematician, physicist, and philosopher whose experimental and theoretical work influenced hydrostatics and barometry. The adoption of the pascal as the SI unit followed developments in metrology and the formalization of the metre and kilogram carried forward by commissions and congresses such as the General Conference on Weights and Measures and organizations like the Comité International des Poids et Mesures. Historical instruments and experiments associated with Pascal’s work intersect with archives and collections at institutions like the Musée des Arts et Métiers, the Bibliothèque nationale de France, and academic departments at the Collège de France and the Sorbonne.
Relation to other units and conversions
The pascal relates to multiple traditional and derived units: 1 Pa = 1 N·m⁻2 = 1 kg·m⁻1·s⁻2. Common multiples and subdivisions include kilopascal and megapascal. The pascal converts to non‑SI units frequently used in specific fields: 1 Pa ≈ 0.00001 bar used in meteorology and oceanography, 1 Pa ≈ 0.0075006 mmHg tied to manometry and clinical pressure measurements, and 1 Pa ≈ 0.000145038 psi encountered in engineering practice in regions influenced by institutions like ASTM International and the American National Standards Institute. Relations to energy densities and elastic moduli connect the pascal to the joule per cubic metre and to units employed in materials testing at laboratories such as the École Polytechnique and the Massachusetts Institute of Technology.
Applications and examples
Practical uses span atmospheric science, where atmospheric pressure is reported in hectopascals in observations by services such as the National Oceanic and Atmospheric Administration, the Met Office, and Météo‑France; civil and mechanical engineering, where soil pressure, foundation loading, and bearing stresses are expressed in kilopascals and megapascals in guidelines from engineering societies like the Institution of Civil Engineers and the American Society of Civil Engineers; and materials science, where tensile and compressive stresses and modulus values are reported in megapascals and gigapascals in journals published by the Royal Society and the American Physical Society. Medical instrumentation for blood pressure and intraocular pressure trace calibrations to pascal-related units used in hospitals affiliated with institutions such as Johns Hopkins Hospital and Great Ormond Street Hospital. Geophysics and oceanography use pascals to quantify lithostatic pressure and hydrostatic pressure in studies by organizations like the United States Geological Survey, the Scripps Institution of Oceanography, and the Alfred Wegener Institute.
Measurement and instrumentation
Measurement of pressure in pascals employs transducers, manometers, and dead‑weight testers calibrated against primary standards maintained by national metrology institutes including the National Metrology Institute of Japan, the Conseil National de Recherches, and the Swiss Federal Institute of Metrology. Instruments such as piezoelectric sensors, strain‑gauge transducers, capacitance manometers, and optical interferometric devices are used in laboratories at CERN, NASA, and industrial test facilities certified by Lloyd’s Register. Calibration chains often reference vacuum standards, piston gauges, and transfer standards traceable to the SI through procedures promulgated by the International Electrotechnical Commission and the International Organization for Standardization.
Standards and notation
Symbolic and typographic practice prescribes the symbol Pa (capital P, lower‑case a) without a trailing period in English usage, consistent with SI brochure recommendations and editorial policies of publishers like Springer and Elsevier. Compound units employ SI prefixes (kPa, MPa, GPa) and follow rules from the International Organization for Standardization and the International Bureau of Weights and Measures on unit names, capitalization, and pluralization. Standards documents from ISO, IEC, and national standards bodies govern presentation, calibration, and uncertainty reporting for measurements expressed in pascals in technical reports, regulatory filings, and academic publications.