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What is Motion?

When we walk on a road remove from one position to another. It means that we are in motion. When we kick a football, it moves from one position to another before it stops finally. It means that the football is in motion.

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Definition of Motion:

When a body changes its position with time as compared to a stationary body, it is said to be in motion. Motion is the continuous change in position of a body with respect to another body.

An apple falling from a tree is changing its position with time as compared to the stationary tree. The apple is said to be in motion relative to the tree.

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A person traveling in a moving train is at rest with respect to his fellow passengers in the same compartment but is in motive with respect to the trees standing along the railway line.

In many cases, it is not difficult to observe the movement of objects. But in some cases, this is quite difficult. For example, the earth is in continuous motion around the sun while also rotating about its own axis. But it is quite difficult to feel this motion because we are moving along with the surrounding objects on the earth.

Types of Motion

All motions are not alike. There are various types of motions. These are:

1. Translatory Motion:

When a car moves, it moves as a whole. All the points in the car move through the same distance in the same time. The car is said to have translatory motion.

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Types of translatory motions: There are two types of translatory motions.

Linear motion: A body moving along a straight line is said to have a linear motion. It is also called rectilinear motion. A stone dropped from a height is an example of linear motion.

Curvilinear motion: A body moving along a curve is said to have a curvilinear motion. A moving car taking a turn is an example of curvilinear motion.

2. Circular Motion:

A body moving along a circular pat is said to have a circular motion.

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The distance of the moving body remains constant from a fixed point or axis, called the axis of rotation. The moving body changes its position during the motion.

A ball tied to a string and whirled around in a circle over the head describes circular motion about a fixed point. A boy running along a circular track describes circular motion. Motion of people sitting in a giant wheel is an example of circular motion. When a fan is switched on, tips of the blades move along a circular path.

Moon follows a circular path while it moves round the Earth. It is a natural example of circular motion. Another natural example is that of the Earth which moves round the sun.

3. Rotatory Motion:

Rotatory Motion is that motion in which a body moves along a circular path about a fixed axis without changing its position.

Examples of rotatory motion are the potter’s wheel and the spinning top. The parts of the potter’s wheel perform a circular motion but the position of the wheel does not change. Each point on the spinning top describes a circular motion while the top remains at its position during the motion.

The Earth rotates (or spins) on its axis. Due to this rotatory motion of the Earth, day and night occur. It must be emphasized that rotatory motion is not quite the same as circular motion. In rotatory motion, the body as whole does not change its position while in circular motion the body itself changes its position and keeps moving along a circular path. We consider a spinning top as having a rotatory motion but not a circular motion.

4. Oscillatory Motion:

Oscillatory motion is that motion in which body repeatedly moves to-and-fro about a fixed point. The fixed point is called the mean position. This kind of motion is also known as vibratory motion.

5. Periodic Motion:

Periodic motion is the motion in which the moving body returns to the same condition after regular (fixed) intervals of time.

Some examples of periodic motion are:

  • The motion of the Earth round the sun is periodic because it always completes one revolution in one year.
  • The motion of the earth rotating on its axis once in 24 hours is a kind of periodic motion because the time duration of 24 hours is fixed.
  • The moon takes 27.3 days to complete a revolution around the Earth.
  • The hands of a clock take the same intervals of time to complete each round. Such a motion is called periodic circular motion.
  • The motion of a swing or a pendulum is periodic and is called periodic oscillatory motion.
  • Heartbeat
  • Pulse movement

All oscillatory motions which repeat after equal intervals of time are periodic motions. But all periodic motions are not oscillatory motions. The oscillatory motion of the feathers of a flying bird need not be periodic.

An athlete moving along a circular path may run fast initially but slow down later when he feels exhausted. In other words, the time taken to complete one round is not the same. This motion is not periodic.

6. Random Motion.

When the motion of the object is not along a fixed path and keeps on changing the direction, the motion is called a random motion.

Some examples of random motion are:

  • Motion of a bird flying in the sky
  • Motion of a hockey ball during a game of hockey or motion of football during a football match.

Sometimes an object may have a combination of more than one type of motion at the same time. Examples of such a motion are given below.

  • The wheels of a car rotate (rotatory motion) and at the same time move forward in a straight or curved path (translatory motion). A combination of rotatory and translatory motions is called rolling.
  • A screw turned by a screwdriver has linear as well as circular motions.
  • Earth rotates about its own axis and also revolves around the sun at the same time. It has rotatory as well as circular motions.
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