# Periodic Motion

PhysicsMotion

#### Class 11th Physics - Elasticity

6 Lectures 1 hours

#### Class 11th Physics - Oscillations

12 Lectures 2 hours

#### Class 11th Physics - Waves

14 Lectures 3 hours

## Introduction

Any kinds of movements or changes that are noticed with respect to the time and position of a body in motion. However, motion or movement can take place on a straight line or it may be within a circular pathway. The motion is known as a translation if the body is said to be moving in a straight or a curved line. On the other hand, the motion that changes the body orientation is known as rotational movements. It is noted that both these two types of motions are noticed in general kinds of examples such as bouncing balls, rocking chairs, etc.

## Definition and types of motion

### Definition

Motion with respect to the body can be defined as the movement of the body from one place to another within a period of time. It needs to be noticed that the body is not in a stationary state (Hyperphysics.phy-astr.gsu.edu, 2022).

• In simple words, if the body changes its position with time then it is said the body is in motion or moving, for example, flying birds, moving trains, cars in motion, walking crowds, and marching of soldiers. However, they are said to be in motion as they are constantly changing their position with time and are opposite to stationary objects, such as a tree, school, electric pole, or factory.

Figure 1: Motion experienced by a body

## Types of Motions

There are several types of motions noticed, which are as follows,

Rectilinear motion - The motion that is said to be occurring in a fixed direction is known as rectilinear motion.

Circular motion - The motion that is said to occur in a circular pathway is referred to as circular motion.

Rotational motion - It is said to be in rotational motion when the body spins or turns within a fixed axis.

Periodic motion - The motion that repeats itself within a specific interval of time is said to be periodic motion.

Figure 2: Types of Motion

## What is Periodic motion?

Periodic motion can be defined as the motion when the body tends to repeat its motion under a specific period of time. The body tends to follow the same pathway, continuously repeating itself, from moving back and forth, or it can be conducted within a circular pathway. It is to be noted that the pathway that is followed by the body in periodic motion can be linear, complex, circular and elliptical.

## A special case of Periodic motion

Figure 3: Simple Harmonic motion of a pendulum

A special case of periodic motion is Simple Harmonic motion or SHM '', which was first mentioned by Copernicus, in his book, De Revolutionibus Orbium Coeles- tium. However, Joseph Fourier first discovered this concept of SHM. In specific, SHM is an oscillatory motion, where the object is moving within a fixed pathway repeating itself (Hyperphysics.phy-astr.gsu.edu, 2022). Moreover, SHM can be said when a body moves along a straight pathway within two extreme points.

• For example, in the case of the pendulum, the phenomenon of SHM is evident. In the given figure number 3, the bob is suspended with a thread from point T and it seems to follow a specific pathway touching two extreme points A and B. The point O is referred to as a stationary equilibrium point. The bob tends to move from position A to B, making one vibration then, from B to A repeating the motion.

## Causes of periodic motion

The main cause that results in periodic motion is the Law of Inertia. The Law of Inertia, states that the body will be in a stationary state or in motion in a straight line with a constant speed, except a force is acted upon the body (Selftution.com, 2022).

The impact of gravitational force is responsible for the cause of periodic motion. The cause for periodicity also depends on the length of the wire.

## Examples of periodic motion

In our day to day life, we experience several kinds of periodic motions, such as movement that is noticed in a rocking chair. The motion of the bouncing ball, vibrations experienced in a tuning fork, and motions that are noticed within swings and also rotation of earth around the sun, movements of the water waves.

Figure 4: Bouncing of a ball displaying periodic motion

In the above figure number 4, a bouncing ball is shown displaying the periodic motion, which states the ball is changing its position within a particular interval of time. However, the movement experienced within a clock is also suggested as periodic as the hands of the clock seem to repeat themselves after a particular interval of time.

## Basic properties of periodic motions

The three major characteristics that are noticed within the phenomenon of periodic motion are, velocity, period and amplitude. The term velocity can be defined as the vector quantity and is the rate of the change in the notion of displacement with respect to direction. Both the examples of bouncing balls and the bob of a pendulum have velocity. The period is defined as the time taken by the object to make the to and fro motion. In the case of the pendulum, the ball seems to conduct the to and fro periodic motion (Oxscience.com, 2022). Amplitude is defined as the maximum displacement within the points of extremes and the resting points. However, the amplitude of the pendulum is the distance that is traversed from the stationary points and extreme ends of the pendulum.

## Understanding Restoring force

Restoring force can be defined as the force that acts on the body to bring it to a state of equilibrium. The restoring force needs to act opposite to the force of displacement, which will support to bring the body in its stationary state or rest position. However, the magnitude of the force depends on the notion of displacement. SHM also displays the phenomenon of restoring force. It needs to be noted that the restoring force will be proportional to the displacement noticed and that the restoring force acts opposite to the direction of the potion for the object.

## Conclusion

Motion is quite an important phenomenon in the field of physics as this defines the stationary and non-stationary moments acknowledged in real life. Both rotational and translational motions are noted within their movements. Four types of motions are noticed, of which periodic motions are quite significant as they determine the movement of the earth around the sun, swinging pendulum. However, it needs to be noted that periodic motion cannot always be oscillatory motion; oscillatory motions are always periodic motions.

## FAQs

Q1. What are the applications of periodic motions?

The clock is one of the most common devices where the phenomenon is displayed. Other ways applications are, wave motions, light, music, and sounds.

Q2.What is the unit of frequency?

The unit of frequency is known as Hertz.

Q3.What are the examples of rotating motions?

Examples of rotational motions are merry go round, sewing machines, bicycles and so on.

Q4.What is non-repetitive motion?

When the body does not follow any particular time to conduct its motions, it is said to be non-repetitive motion.

Reference

## Websites

Hyperphysics.phy-astr.gsu.edu, (2022), Periodic Motion, Retrieved from: http://hyperphysics.phy-astr.gsu.edu [Retrieved on: 7th June 2022]

Oxscience.com, (2022), Motion in Physics, Retrieved from: https://oxscience.com [Retrieved on: 7th June 2022]

Practically.com, (2022), Motion and Time, Retrieved from: https://www.practically.com [Retrieved on: 7th June 2022]

Selftution.com, (2022), Types of Motion in Physics with Examples, Retrieved from: https://selftution.com [Retrieved on: 7th June 2022]

Updated on 13-Oct-2022 11:19:47

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