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A millimetre of mercury is a manometric unit of pressure, formerly defined as the extra pressure generated by a column of mercury one millimetre high. Currently, it is defined as exactly 133.322 387 415 pascals, or approximately [a] 1 torr = 1 / 760 atmosphere = 101 325 / 760 pascals. [1] [2] It is denoted mmHg [3] or mm Hg. [4] [2]
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 unit for pressure is the pascal (Pa), equal to one newton per square metre (N/m 2, or kg·m −1 ·s −2). This name for the unit was added in 1971; [7] before that, pressure in SI was expressed in newtons per square metre. Other units of pressure, such as pounds per square inch (lbf/in 2) and bar, are also in common use.
Symbol Name Meaning SI unit of measure alpha: alpha particle: angular acceleration: radian per second squared (rad/s 2) fine-structure constant: unitless beta: velocity in terms of the speed of light c: unitless beta particle: gamma: Lorentz factor: unitless photon: gamma ray: shear strain: radian
Quantity Unit Remarks Name Symbol Name Symbol Definition Force: F: newton: N 1 N = 1 kg·m/s 2: Unit named after Isaac Newton: Moment of force, Torque: M, : N·m 1 N·m = 1 kg·m 2 /s 2: The unit is dimensionally equivalent to the units of energy, the joule; but the joule should not be used as an alternative for the newton metre.
The fermi is a unit of distance used in nuclear physics equal to 1 fm. [9] The angstrom (symbol Å) is a unit of distance used in chemistry and atomic physics equal to 100 pm. The micron (μ) is a unit of distance equal to one micrometre (1 μm). The basic module (M) is a unit of distance equal to one hundred millimetres (100 mm).
The symbol (uppercase) should be used with prefix symbols (thus, mTorr and millitorr are correct, but mtorr and milliTorr are not). The torr is sometimes incorrectly denoted by the symbol "T", which is the SI symbol for the tesla, the unit measuring the strength of a magnetic field. Although frequently encountered, the alternative spelling "Tor ...
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.