General Physics I:

If a body repeats its motion after a fixed interval of time, then the body is said to be in periodic motion. In periodic motion object returns to its original position at some later time. The motion of the wheels, rocking chair, bouncing ball, a swing in motion, water waves, motion of planets around the sun, motion of clock arms, motion of spring-mass system, and motion of simple pendulum, etc. are some examples of periodic motion. If a body retraces its original path over and over about a mean position, then the body is in oscillatory motion. In oscillatory motion body moves to and fro (or back and forth) repeatedly about a fixed mean (equilibrium) position. Motion of a simple pendulum, spring-mass system, vibrating tuning fork, rocking chair, etc are some examples of oscillatory motion. A restoring force is responsible for oscillatory motion. A ball displaced a little from its rest position in a bowl performs an oscillatory motion. Circular motion of clock arms or wheels, etc. is periodic but not oscillatory. The wheels or clock arms do not move back and forth about the mean position rather they are moving in a circular motion is periodic not oscillatory. The motion of a pendulum is both oscillatory and periodic. All oscillatory motion is periodic but not all periodic motion is oscillatory. The motion of simple pendulum, spring - mass system, etc. is both oscillatory and periodic but the motion of wheels, motion of clock arm, planetary motion, etc. is only periodic. In periodic motion body also regain its all parameters after equal interval. The particles of a body get same velocity and direction at the same point over and over. If not then it becomes a random motion. In oscilattory motion, particle changes its direction of velocity at each point during the course of motion.