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.
There are three types of motion.
(I) Translatory motion (linear, random and circular)
(ii) Rotatory motion
(iii) Vibratory motion (to and fro motion)
i) TRANSLATORY MOTION
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 translational motion. Similarly, an aeroplane moving straight is in translational motion.
In translational motion, a body moves along a line without any rotation. The line may be straight or curved.
The object as shown in figure below moves along a curved path without rotation. This is the translational motion of the object. Riders moving in
a Ferris wheel such as shown in figure below are also in translational motion. Their motion is in a circle without rotation. Translatory motions can be divided into linear motion, circular motion and random 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 a car moving on a straight and level road is linear motion.
Aeroplanes flying straight in air and objects falling vertically
down are also the examples of linear motion.
The motion of an object in a circular path is known as circular motion.
A stone tied at the end of a string can be made to whirl. What type of path is followed by the stone? A stone tied at the end of a string moves in a circle.
Figure below shows a toy train moving on a circular track. A bicycle or a car moving along a circular track possesses circular motion. Motion of the Earth around the Sun and motion of the moon around the Earth are also the examples of circular motions.
The disordered or irregular motion of an object is called random motion.
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 path such as shown in figure is also an example of random motion.
ii) ROTATORY MOTION
The spinning motion of a body about its axis is called its rotatory motion.
Study the motion of a top. 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 shown in figure spins about its axis passing through it and thus it possesses 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 line, around which a body moves about, is passing through the body itself.
Can you point out some more differences in circular and rotatory motion?
The motion of a wheel about its axis and that of a steering wheel are the examples of rotatory motion. The motion of the Earth around the Sun is circular motion and not the spinning motion. However, the motion of the Earth about its geographic axis that causes day and night is rotatory motion. Think of some more examples of rotatory motion.
iii) VIBRATORY MOTION
Consider a baby in a swing as shown in figure below. 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.
To and fro motion of a body about its mean position is known as vibratory motion.
Figure shows to and fro motion of the pendulum of a clock about its mean position, it is called vibratory motion. We can find many examples of vibratory motion around us.