# Periodic Motion

A motion which repeats itself over and over again after a regular interval of time is called periodic motion and the fixed interval of time after which the motion is repeated is called period of the motion.

# Oscillatory or Vibratory Motion

Oscillatory or vibratory motion is that motion in which a body moves to and fro or back and forth repeatedly about a fixed point in a definite interval of time. In such a motion, the body is confined with in well-defined limits on either side of mean position. Oscillatory motion is also called as harmonic motion.

# Harmonic and Non-Harmonic Oscillation

Harmonic oscillation is that oscillation which can be expressed in terms of single harmonic function (i.e., sine or cosine function).

**Example**,*y*=*Î±*sin*Ï‰t*or*y*=*Î±*cos*Ï‰t*.Non-harmonic oscillation is that oscillation which can not be expressed in terms of single harmonic function. It is a combination of two or more than two harmonic oscillations.

**Example**,*y*=*Î±*sin*Ï‰t*+*b*sin 2*Ï‰t*