Measurement
Dictionary of Principal Units

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-P-

PARSEC (psc)

A unit of distance. One parsec equals 3.08 57 x 10¹⁶ meters or 3.26 16 light years.

PASCAL (Pa)

A unit of pressure or stress. One pascal equals 1 newton per square meter.

PHON (phon)

A unit of loudness level. The pressure level in decibels of a pure 1 000 Hz tone.

PHOT (ph)

The CGS unit of illuminance. One phot equals 1 lumen per square centimeter. Use of the SI unit, the lux, is preferred.

PINT (pt)

A unit of volume in the "English" system. One pint equals 2 cups or 0.5 quart. Because the gallon, quart, and pint differ in the United States and the United Kingdom, the use of this unit and term is generally discouraged for scientific purposes. One U.S. pint equals: (1) 473.2 cubic centimeters; (2) 0.016 71 cubic foot; (3) 28.87 cubic inches; (4) 4.732 x 10^-4 cubic meter; (5) 6.189 x 10^-4 cubic yard; (6) 0.125 U.S. gallon; (7) 0.4732 lilter; or (8) 0.5 U.S. quart.

POISE (P)

The CGS unit of dynamic viscosity. The unit is expressed in dyne second per square centimeter. The centipoise (cP) is more commonly used.

The formal definition of viscosity arises from the concept put forward by Newton that under conditions of parallel flow, the shearing stress is proportional to the velocity gradient. If the force acting on each of two planes of area A parallel to each other, moving parallel to each other with a relative velocity V, and separated by a perpendicular distance X, be denoted by F, the shearing stress is F/A and the velocity gradient, which will be linear for a true liquid, is V/X. Thus, F/A = nV/X, where the constant n is the viscosity coefficient or dynamic viscosity of the liquid.

POUND (lb)

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POUNDAL (pdl)

A unit of force in the "English" system. One poundal equals the force required to give a standard 1- pound body an acceleration of 1 foot per second per second.

-Q-

QUART (qt)

A unit of volume in the "English" system. One quart equals 2 pints or 0.25 gallon. Because the gallon, quart, and pint differ in the United States and the United Kingdom, the use of this unit and term is generally discouraged for scientific purposes. One U.S. quart equals: (1) 946.4 cubic centimeters; (2) 0.033 42 cubic foot; (3) 57.75 cubic inches; (4) 9.464 x 10^-4 cubic meter; (5) 1.238 x 10^-3 cubic yard; (6) 0.25 U.S. gallon; or (7) 0.9463 liter.

-R-

RAD (rd)

A unit of absorbed dose of radiation. One rad equals the absorption of energy in any medium of 100 ergs per gram.

RADIAN (rad)

The SI unit of plane angle. One radian equals the angle subtended at the center of a circle by a circular arc which is equal in length to the radius of the circle.

RANKINE(^oR)

A unit of temperature. See DEGREE RANKINE

REM (rem)

A unit of radiation dose equivalent. One rem equals the amount of ionizing radiatio of any type which produces the same damage to humans as 1 roentgen of approximately 200 kilo volts x-radiation. (The unit is the abbreviation of Roentgen Equivalent Man.)

REVOLUTION PER MINUTE (r/min)

A unit of frequency. Although use of rpm as an abbreviation is common, it's use as a symbol is discouraged.

ROENTGEN (R)

A unit of radiation exposure. That quantity of x- or gamma-radiation such that the associated corpuscular emission per 0.001 293 gram of dry air (equals 1 cubic centimeter at 0^oC and pressure 769 millimeters of mercury) produces in air ions carrying 1 esu of electricity of either sign.

-S-

SECOND (s)

The SI unit of time. The second was defined originally as 1/86 400 of the mean solar day. Because a more precise definition was needed, the 13^th General Conference on Weights and Measures (CGPM 1967) replaced the astronomical definition of the second by the following:

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.

SLUG (slug)

A unit of mass in the "British" system. One slug equals 14.59 59 kilograms or 32.174 pounds.

STERADIAN (sr)

A unit of solid angle. One steradian equals the solid angle subtended at the center of a sphere by 0.25PI of the surface area of a sphere of unit radius.

STILB (sb)

A unit of luminance. One stilb equals 1 candela per square centimeter.

STOKES (St)

A unit of kinematic viscosity. The centistoke (cSt) is more commonly used. Kinematic viscosity is the dymanic viscosity divided by the density. Related to the poise.

-T-

TESLA (T)

The SI unit of magnetic flux (flow) density (magnetic induction). The magnetic flux density of a uniform field that produces a torque of 1 newton- meter on a plane current loop carrying 1 ampere and having projected area of 1 square meter on the plane perpendicular to the field. (T = N/A m)

THERM (thm)

A unit of heat. One therm equals 100 000 (10⁵) British thermal units.

TON (ton)

A unit of weight. If not otherwise specified, a short ton equal to 2 000 pounds is assumed. A long ton equals 2 240 pounds. A metric ton equals 1 000 kilogams (2 205 pounds), also called a tonne (t).

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