# Frequency

(Redirected from Frequencies) Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency.

## Definitions and units

For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles, or periods, per unit time. In physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by a Greek letter ν (nu).

In SI units, the unit of frequency is hertz (Hz), named after the German physicist Heinrich Hertz. For example, 1 Hz means that an event repeats once per second.

A traditional unit of measure used with rotating mechanical devices is the revolutions per minute, abbreviated rpm. 60 rpm equals one hertz.

The period is usually denoted as T, and is the reciprocal of the frequency f:

The SI unit for period is the second.