Primary
Pressure (p) ○◂｜Definition｜1st｜20251119205401-00-⌔
Pressure
Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.1 Gauge pressure (also spelled gage pressure)2 is the pressure relative to the ambient pressure.
Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m); similarly, the pound-force per square inch (psi, symbol lbf/in) is the traditional unit of pressure in the imperial and US customary systems. Pressure may also be expressed in terms of standard atmospheric pressure; the unit atmosphere (atm) is equal to this pressure, and the torr is defined as 1 ⁄ 760 of this. Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.
Printed 2026-06-28.
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Link to original Footnotes
*Knight, Randall D. (2007). “Fluid Mechanics”. Physics for Scientists and Engineers: A Strategic Approach (2nd ed.). San Francisco: Pearson Addison Wesley. p. 1183. ISBN 978-0-321-51671-8. Retrieved 6 April 2020. Pressure itself is not a Force, even though we sometimes talk “informally” about the “force exerted by the pressure. The correct statement is that the Fluid exerts a force on a surface. In addition, Pressure is a scalar, not a vector. * ↩
The preferred spelling varies by country and even by industry. Further, both spellings are often used within a particular industry or country. Industries in British English-speaking countries typically use the “gauge” spelling. ↩
Secondary
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