define motion and periodic motion

An object is said to be in motion if it changes it's position with time,with respect to it's surroundings.

For example - A car moving on a road possesses motion.

Periodic motion is that motion which repeats itself after equal intervals of time. The interval of time is called the time period of periodic motion. Example: (i) motion of planets around the sun (ii) motion of the pendulum of a wall clock (iii) motion of the hands of a clock etc.