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.
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 ? (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, 2 Hz is twice per second, and so on. This unit was originally called a cycle per second (cps), which is still sometimes used. Heart rate and musical tempo are measured in beats per minute (BPM). Frequency of rotation is often expressed as a number of revolutions per minute (rpm). BPM and rpm values must be divided by 60 to obtain the corresponding value in Hz thus, 60 BPM translates into 1 Hz.
The period is usually denoted as T, and is the reciprocal of the frequency f
