Periodic signals
Vibrations

A signal is periodic if it recurs identically at strictly equal time intervals (e.g. gravity pendulum, mass suspended from a spring, etc.).

The period T is the shortest time interval between two signal passages through the same position and in the same direction.

The frequency ν is the inverse of the period T; it is expressed in hertz (Hz).

A periodic phenomenon can be described in different ways, with or without the presence of discontinuities (§ 1.1.2