Question

How to identify periodic and non-periodic motion?

Answer 1

Hint: Any event that repeats itself after fixed intervals of time is called a periodic event.

Complete step by step answer:
 Any form of motion that repeats itself after fixed intervals of time is called a periodic motion, while one that does not repeat itself after fixed intervals of time is defined as a non-periodic motion.

For example, the earth takes 365 days to revolve around the sun and 24 hours to rotate once about its axis. These two motions can be termed as periodic motions since they repeat itself after specific intervals of time. It is fixed that after every 24 hours, the earth proceeds to complete another full rotation about its axis. The motion of all planets is periodic in nature.

On the other hand, events that occur randomly and have no fixed time after which they may repeat again are non-periodic in nature. The motion of a shark chasing a small fish is random and non-periodic. The shark and fish do not repeat their motions after fixed intervals of time.

Additional information:
Periodic motions have different definite features such as their time period and frequency.
The time period of a periodic motion is the time taken to complete one full cycle of the motion. It is the time after which the motion repeats.
The frequency of a periodic motion is the number of times the motion has been completed in one second.
Thus, time period and frequency are the inverse of each other.
Time period is denoted as ‘T’ and measured in seconds (SI unit), while frequency is denoted as ‘f’ and measured in seconds-1 (SI unit).
$T=\dfrac{1}{f}$

Note: Students may get confused between oscillatory and periodic motion. However, oscillatory motion is just a form of periodic motion in which the body moves to and fro about a point in one time period.
On the other hand, a periodic motion refers to any movement in any dimension that repeats periodically.
Thus, it can be said that ‘All oscillatory motions are periodic, but all periodic motions are not oscillatory’.