Rotational frequency , also known as rotational speed or rate of
rotation (symbols ν , lowercase Greek nu, and also n ), is the frequency
of rotation of an object around an axis. Its SI unit is the reciprocal seconds
(s−1); other common units of measurement include the hertz (Hz), cycles per
second (cps), and revolutions per minute (rpm).
Rotational frequency can be obtained dividing angular frequency , ω, by a
full turn (2π radians): ν =ω/(2π rad). It can also be formulated as the
instantaneous rate of change of the number of rotations, N , with respect to
time, t : n =d N /d t (as per International System of Quantities, ISO
80000-3).