What is oscillatory motion

The to and fro of a pendulum

Every body at rest is in its equilibrium position. At this position, no external force is acting on it. Therefore, the net force acting on the body is zero. Now, if this body is displaced a little from its equilibrium position, a force acts on the body which tries to bring back the body to its equilibrium position. This force is the restoring force and it gives rise to oscillations or vibrations. For example, consider a ball that is placed in a bowl. It will be in its equilibrium position. If displaced a little from this position, it will perform oscillations in the bowl. Therefore, every oscillatory motion is periodic but all periodic motions are not oscillatory. Circular motion is a periodic motion but not oscillatory motion.