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# Definition of motion in physics:

“A body is said to be in motion,if it changes its position with respect to its surroundings.”

Surroundings are the places in its neighborhood where various objects are present.The state of rest or motion of a body is relative.For example,a passenger sitting in a moving bus is at rest because he is not changing his position with respect to other passengers or objects in the bus.But to an observer outside the bus,the passengers and the objects inside the bus are in motion.Therefore we can defined rest as “A body is said to be at rest ,if it does not change its position with respect to its surroundings.”

We live in a universe of continual motion.In every piece of matter, the atoms are in state of never ending motion.We move around the Earth’s surface ,while the earth moves in its orbit around the sun.The sun and the stars ,too,are in motion.Everything in the vastness of space is in a state of perpetual motion.Every physical process involves motion of some sort.Because of its importance in the physical world around us.It is logical that we should give due attention to the study of motion.Motion is commonly described in terms of:

## What are the different types of motion?

If we observe carefully,we will find that everything in the universe is in motion.However ,different objects move differently.Some objects move along a straight line,some move in a curved path,and some move in some other way.According to this we can say that there are three types of motion.Which are given as:

• Translatory motion
• Rotatory motion
• Vibratory motion
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## Translatory motion:

“In transnational motion,a body moves along a line without any rotation.The line may be straight or curved.”Watch how various objects are moving.Do they move along a straight line?Do they move along a circle?A car moving in a straight line has transnational motion.Similarly,an aeroplane moving straight is in transnational motion. Translatory motion is further divided into linear motion,circular motion and random motion.

### Linear motion:

“Straight line motion of a body is known as its linear motion.”

We come across many objects which are moving in a straight line.The motion of objects such as car moving on a straight and level road is linear motion. Aeroplanes flying straight in air and objects failing vertically down are also the examples of linear motion.

In the above diagram a boy is sliding in straight line which is the example of linear motion.

### Circular motion:

“The motion of an object in a circular path is known as circular motion.”A toy train moving on a circular track.Earth revolving around the sun is the example of circular motion.

A bicycle or a car moving along a circular track possesses circular motion.Motion of moon around earth is also example of circular motion.Planets revolve around the sun,is circular motion.Electrons revolve also around the nucleus possesses circular motion.

### Random motion:

“The disordered or irregular motion of a body is called random motion.”Have you noticed the type of motion of insects and birds?Their movements are irregular and disorder.Motion of insects and birds is random motion.The motion of dust or smoke particles in the air is also random motion.The Brownian motion of a gas or liquid molecules along a zig – zag is also an example of random motion.”Random motion of gas molecules is called Brownian motion.”

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## Rotatory motion:

“The spinning motion of a body about its axis is called its rotatory motion.”Study the motion of a tap.It is spinning about an axis.Particles of the spinning top move in circles and thus individual particles possess circular motion.Does the top possess circular motion?The top spins about its axis passing through it and thus it possess rotatory motion.An axis is a line around which a body rotates.In circular motion ,the point about which a body goes around ,is outside the body.In rotatory motion,the lone ,around which a body moves about,is passing through the body itself.

The motion of the earth about its geographic axis that causes day and night is rotatory motion.While the motion of the earth around the sun is circular motion.The motion of wheel about its axis and that of steering wheel are the examples of rotatory motion.

## Vibratory motion:

“The motion of a body about its mean position is known as vibratory motion.”

Consider a baby in a swing as shown in above figure.As it is pushed,the swing moves back and forth about its mean position.The motion of the baby repeats from one extreme to the other extreme with the swing.Motion of pendulum of a clock about its mean position,is also example of vibratory motion.Children playing in a sea saw is the example of vibratory motion.Besides these examples a baby in a cradle moving to and fro,to and fro motion of the hammer of a ringing electric bell and the motion of the string of a sitar are some of the examples of vibratory motion.Simple harmonic motion is also example of vibratory motion.

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