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The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI). It is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is an SI coherent derived unit defined as one newton per square metre (N/m 2). [1]
The SI has special names for 22 of these coherent derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m 2), the SI derived unit of area; and the kilogram per cubic metre (kg/m 3 or kg⋅m −3), the SI derived unit of density. The names of SI ...
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 2); similarly, the pound-force per square inch (psi, symbol lbf/in 2) is the traditional unit of pressure in the imperial and US customary ...
A combination of base and derived units may be used to express a derived unit. For example, the SI unit of force is the newton (N), the SI unit of pressure is the pascal (Pa) – and the pascal can be defined as one newton per square metre (N/m 2). [6]
Two of the base SI units and 17 of the derived units are named after scientists. [2] 28 non-SI units are named after scientists. By this convention, their names are immortalised. As a rule, the SI units are written in lowercase letters, but symbols of units derived from the name of a person begin with a capital letter.
Rate of change of crackle per unit time: the sixth time derivative of position m/s 6: L T −6: vector Pressure gradient: Pressure per unit distance pascal/m L −2 M 1 T −2: vector Temperature gradient: steepest rate of temperature change at a particular location K/m L −1 Θ: vector Torque: τ
Other units of pressure include: The bar (symbol: bar), defined as 100 kPa exactly. The atmosphere (symbol: atm), defined as 101.325 kPa exactly. These four pressure units are used in different settings. For example, the bar is used in meteorology to report atmospheric pressures. [7] The torr is used in high-vacuum physics and engineering. [8] [9]
where (in SI units): q is the dynamic pressure in pascals (i.e., N/m 2, ρ (Greek letter rho) is the fluid mass density (e.g. in kg/m 3), and; u is the flow speed in m/s. It can be thought of as the fluid's kinetic energy per unit volume. For incompressible flow, the dynamic pressure of a fluid is the difference between its total pressure and ...