Define periodic motion and oscillatory motion.

(N/A) $1$. Periodic Motion: $A$ motion that repeats itself at regular intervals of time is called periodic motion. For example,the revolution of the Earth around the Sun or the motion of the hands of a clock.
$2$. Oscillatory Motion: $A$ motion in which a body moves to and fro or back and forth about a fixed point (mean position) is called oscillatory motion. For example,the motion of a simple pendulum or the vibration of a string in a musical instrument.
Note: All oscillatory motions are periodic,but not all periodic motions are oscillatory.