Law of Inertia - Definition, Types, Examples, FAQs

What is the law of inertia with examples?

The Law of Inertia states that an object will remain at rest or continue to move in a straight line with constant speed unless acted upon by an external unbalanced force.

In simple words, it means that objects resist any change in their state of motion. This law is also known as Newton’s First Law of Motion.

Example:
A book on a table stays still until someone pushes it. Similarly, a moving ball keeps rolling until friction or another force stops it.

Types of Inertia

Inertia is the resistance of the body to any change in its velocity.

There are Three Types of Inertia Force

1. Inertia of Rest: The body's tendency to stay in a state of rest. The body usually stays at rest until external energy is used to move. Therefore, inertia of rest is the body's inability to move and remain in a state of rest.

Example: When we hit the carpet, it comes in motion, with dust particles in the resting state. This is because dust particles tend to remain restless, which is why they are separated.

2. Inertia of Direction: The tendency of the body to sit on one side. The body usually stays on the same side until the external force acts on it to make a change in its movement.

Examples

1. A bicycle usually travels in a straight line unless it is turning the handle of the bike.

2. When you turn one side of the rope tied to the stone. Suddenly the rope breaks and the stone flies along the tangent to a circle.

As soon as the rope breaks, the pull disappears and the stone flies away in a lovely way.

3. Inertia of motion: The inclination of the body to remain in the same state of motion. A body continues to move in the same direction unless acted by an external force.

examples

Here are a few real-life examples of defining inertia of movement:

1. When the train suddenly stopped, it collapsed. With the inertia of movement, the upper part of the body contacts the seat and begins to move, while the lower part tries to sit still.

2. A man jumps off a train and falls ahead. This is because his feet touch the ground and they stay at rest while the rest of the body moves

Galileo’s Explanation of Inertia:

Galileo was the first scientist to clearly explain the concept of inertia. He stated that an object will continue to move forever in the same direction with uniform speed unless an external force stops it.

He observed that when a ball rolls down a smooth inclined plane and then up another, it rises almost to the same height from which it was released. If friction were completely removed, the ball would continue moving indefinitely.

From this, Galileo concluded that no force is needed to keep an object in uniform motion, and that forces are required only to change the state of motion either to start, stop, or change direction.

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Solved Example Based on Inertia

Example 1:A man is standing in a moving bus. Now he is getting down, he falls forward because -

1) due to the inertia of the rest road is left behind and man reaches forward.

2) due to inertia of motion, the upper part of the body continues to be in motion in the forward direction while the feet come to rest as soon as they touch the road.

3) He leans forward as a matter of habit.

4) None of the above

Solution:

Inertia is the property of a body by which it continues to remain in its existing state of rest or uniform motion in a straight line unless an external force acts on it. So due to inertia of motion, the upper part of the body continues to be in motion in the forward direction while feet come to rest as soon as they touch the road.

Hence when he is getting down from the moving bus, he falls forward.

Hence, the answer is the option (2).

Example 2: A particle is in straight-line motion with uniform velocity. A force is not required:

1) To increase the speed

2) To decrease the speed

3) To keep the same speed

4) To change the direction.

Solution:

Inertia is the property of a body by which it continues to remain in its existing state of rest or uniform motion in a straight line unless an external force acts on it.

A body cannot change its state on its own. So to keep the same speed, a force is not required.

Hence, the answer is the option (3).

Example 3: Given below are two statements: one is labeled as Assertion A and the other is labeled as Reason R

Assertion A: An electric fan continues to rotate for some time after the current is switched off.

Reason R: The fan continues to rotate due to the inertia of motion.

In the light of the above statements, choose the most appropriate answer from the options given below:

1) A is not correct but R is correct

2) Both A and R are correct and R is the correct explanation of A

3) Both A and R are correct but R is NOT the correct explanation of A

4) A is correct but R is not correct

Solution:

Inertia is the property of mass due to which the object continues to move until any external force does not stop it. In the case of the rotation of the fan, if we switch it off then also it moves for some time as air resistance takes time to stop it, and due to the inertia of the fan it moves for some time.

Hence, the answer is the option(2).

Example 4: Why do passengers in a moving train suddenly feel a Shock in the forward direction when the train stops abruptly?

1) The upper body of the passenger continues to be in a state of motion while the lower part of the body which is in contact with the seat remains at rest.

2) The back of the seat pushes passengers forward

3) The inertia of rest stops the train and takes the passengers forward

4) None of these

Solution:

Inertia is the property of a body by which it continues to remain in its existing state of rest or uniform motion in a straight line unless an external force acts on it.

So the passengers in a moving train suddenly feel a Shock in the forward direction when the train stops abruptly because The upper body of the passengers continues to be in the state of motion while the lower part of the body which is in contact with the seat remains at rest.

Hence, the answer is the option (1).