Physics
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Periodic Motion and Non Periodic Motion- Definitions, Formulae

When a body repeats its motion at fixed interval of time, it is said to have periodic motion. Read about periodic and non periodic motions here in detail.

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Posted by Mahak Jain, 25/8/2021
Periodic Motion and Non Periodic Motion- Definitions, Formulae

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To study motion in detail there is a need to classify motion based on different criteria. We can classify the motion of various bodies on the basis of the way they move. For example, a car moving on a straight road exhibit linear motion. Similarly, the motion of the earth around the sun is circular motion. Here, in this blog we will focus on periodic and non periodic motion.

Please note that the term oscillation is wrongly used in place of periodic motion. You, after reading this blog should avoid this mistake. Oscillation is special kind of periodic motion. All oscillations are periodic motion but all periodic motions are not oscillations.

What is Periodic Motion?

A body exhibits periodic motion if it moves such that it repeats its path after regular intervals of time.

Suppose you go to school regularly at exactly 7 am. Then, your motion to school is periodic. Hope you understand the concept of periodic motion. Some examples of periodic motion are in the following image.

Example graphs of periodic motion

To avoid confusion between periodic motion and oscillation, let me explain oscillation here in short.

If the body undergoing periodic motion has an equilibrium position somewhere in between its path, its motion is not simply periodic motion. Rather a special kind of periodic motion. When the body is at this position no net external force acts on it. Therefore, if it is left there at rest, it remains there forever. If we externally displace the body from the position, a force comes into play which tries to bring the body back to the equilibrium point. As a result, giving rise to oscillations or vibrations. For example, a ball placed in a bowl will be in equilibrium at the bottom. If displaced a little from the point, it will perform oscillations in the bowl. Every oscillatory motion is periodic, but every periodic motion need not be oscillatory. Uniform circular motion is a periodic motion, but it is not oscillatory.

Time Period and Frequency of Periodic Motion

We know that periodic motion repeats itself after regular intervals of time. Time period is the smallest interval of time after which the motion repeats. You can call time period as simply period. We use English letter T to represent time period.

The number of times motion repeats in a second is called frequency. It is represented by Greek letter ν.

Thus, Mathematically ν = 1/T.

Examples of Periodic Motion

  • The motion of the hands of a clock. The period of motion of an hour’s hand is 12 hrs, of a minute’s hand is 1 hour and of the second’s hand of a clock is 1 minute.
Pendulum is an example of periodic motion
  • A simple pendulum, when pulled from its rest position to one side. When released from non equilibrium position it makes to and fro motion (oscillatory motion). And we know that oscillatory motion is periodic motion.

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