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INERTIA AND ITS DIFFERENT TYPES
Inertia. The inherent property of a material body by virtue of which it cannot change, by
itself, its state of rest or of uniform motion in a straight line is called inertia.
The term inertia means resistance to change. This term was first used by Galileo.

Different types of inertia:
(i)Inertia of rest. The tendency of a body to remain in its position of rest is called inertia
of rest.
Examples

(i) When a horse suddenly starts running, the rider falls backward. This is because the
lower part of the rider, which is in contact with the horse, comes into motion while his
upper part tends to remain at rest due to inertia.

(ii) Dust is removed from a hanging carpet by beating it with a stick. As the carpet is
beaten, it suddenly moves forward while the dust particles tend to remain at rest due to
inertia of rest and so fall off.

(iii) When we shake the branch of a tree, its fruits and dry leaves fall down. On shaking,
the branch comes into motion while the dry fruits and leaves tend to remain at rest
(inertia of rest) and so get separated.

(iv) Coin falls into the tumbler when the card is given a sudden jerk. Place a five rupees
coin on a playing card covering a glass tumbler. Give a sudden jerk to the card, the card
flies off and the coin drops into the tumbler. This is because the coin tends to remain at
rest due to inertia.
(v)A person standing in a bus falls backward when the bus suddenly starts moving
forward. When the bus moves, the lower part of his body begins to move along with the
bus while the upper part of his body continues to remain at rest due to inertia. That is
why, a person falls backward when the bus starts.

(ii)Inertia of motion. The tendency of a body to remain in its state of uniform motion in
a straight line is called inertia of motion.

Examples
(i) A person getting out of a moving bus or train falls in the forward direction. As the man
jumps out of a moving bus, his feet suddenly come to rest on touching the ground while
the upper part of his body continues to move forward. That is why he falls with his head
forward. In order to save himself from falling down, he should run in the forward
direction through some distance.
(ii) An athlete runs for a certain distance before taking a long jump. The inertia of motion
gained by him at the time of jumping adds to his muscular effort and helps him in taking
a longer jump.