Revolutions per minute velocity. The corresponding basic SI derived unit is s or Hz. When measuring angular speed, the unit radians per second is used. Formally, hertz (Hz) and radian per second (rad/s) are two different names for the same SI unit, s. However, they are used for two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity). The conversion between a frequency (measured in hertz) and an angular velocity (measured in radians per second) are: Thus a disc rotating at 60 rpm is said to be rotating at either 2 rad/s or 1 Hz, where the
Rayleigh (unit) Rayleigh (unit) The rayleigh is a unit of photon flux, used to measure airglow (auroras, for example). It was first proposed in 1956 by Donald M. Hunten, Franklin E. Roach, and Joseph W. Chamberlain. It is named for John William Strutt, 3rd Baron Rayleigh (1842–1919). Its symbol is R (also used for the röntgen, an unrelated unit). SI prefixes are used with the rayleigh. One rayleigh (1 R) is defined as a column emission rate of 10 photons per square metre per column per second. Note that rayleigh is an apparent emission rate, as no allowances have been made for