Law of Inertia - Definition, Types, Examples, FAQs

The Principle of moment of Inertia or the first law of motion may also be referred to as Newton’s first law. It states that an object, once at rest or in straight uniform motion, will continue to do so unless some force comes in from outside to disrupt this status quo. This is a basic reason for understanding the concept of inertia – how do objects oppose any change in motion? Inertia is a phenomenon that is experienced in everyday situations, from the sudden gripping of the seat when a car stops suddenly to the movement of the solar system, which all exist even without the intercession of any motor force. This makes it one of the primary features in the field of physics.

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Law of Inertia Definition?

A body, either in a state of rest or in a state of motion, always tries to resist change. So if an external force is applied to the body, the body will try to resist the force. This inbuilt ability of the body is equal to the mass of the body. It is called inertia. Hence, inertia can be defined as the resistance provided by the body to a change of state, directly proportional to its mass.

Example:

1. When you travel in a vehicle, if the driver presses the brake suddenly, you feel a jerk. This jerk is felt because your body tries to resist the sudden change.

2. Athletes run a certain distance before taking a long jump.

3. When the horse runs full and suddenly stops, the man falls forward.

4. When you move a mango tree, the mango falls from the tree.

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Types of Inertia

Inertia 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

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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 labelled as Assertion A and the other is labelled 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 jerk 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 jerk 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).