Law of Inertia - Definition, Types, Examples, FAQs

Inertia is one of the natural basic phenomena of physics that describes an object's resistance to any change in its state of motion. This is interpreted that an object which is at rest will forever be at rest, and one in motion will remain moving at a uniform speed in a straight line unless an unbalanced force is used. This concept is expressed in Newton's First Law of Motion as well as in the law of inertia.

In this article, we will cover the concept of inertia. This concept falls under the broader category of law of motion which is a crucial chapter in Class 11 physics. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE and more. Over the last ten years of the JEE Main exam (from 2013 to 2023), a total of one question has been asked on this concept.

What is Law of Inertia. State the Law of Inertia.

Newton's first law of motion is also known as the law of inertia.
The law states that the body continues to be in a state of rest or similar movement in a straight line, except when exerted force to change its position.

In our daily lives, we find that the ball rolls down after a while. This is because the force of the ground force works on the ball to make a change in the state of its movement.

Body inertia is measured by body size.

The heavier the size, the greater the power required, so its inertia and vice versa.

Therefore, Newton's first law defines inertia, and is rightly called the law of inertia.

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What is meant by Inertia? What is inertia of physics?

Inertia definition physics or Inertia meaning: The natural feature of all bodies, as a result of which they resist changes in the state of rest or the same movement in a straight line alone is called inertia.

Inertia Examples

Here are a few examples of the law of inertia in our daily lives:

1.When the bus suddenly starts, we fall backward. This is because our lower body begins to move with the bus while the upper part tries to stay relaxed.

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.

5.When the car suddenly turns around, the driver is thrown out.

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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.

2.Inertia of Direction: The tendency of the body to sit on one side.

3.Inertia of motion: The inclination of the body to remain in the same state of motion.

Inertia 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.

Inertia of rest examples

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.

Inertia of Direction

The body usually stays on the same side until the external force acts on it to make a change in its movement.

The inertia of direction examples

Here are a few examples of real-life experiences discussed below:

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 circle.

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

Inertia of Motion

A body continues to move in the same direction and unless acted by an external force.

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Inertia of motion examples

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

1.When the train suddenly stopped, it collapsed. With 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

Do you know?

Before Newton described the three laws of motion, the great Greek philosopher Aristotle argued that external force is needed to keep the body moving. But you have failed to see that the opposing forces work in the body to withstand external forces, so that the net energy in the body is zero.

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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).

Conclusion

Inertia is directly proportional to mass—an object with greater mass possesses greater inertia and requires a commensurately greater force to change its state of motion.

Its applications in force management for sports, machinery, or transport means are also keenly felt. The importance of this principle lies in efficient system design and safety implementation and is unparalleled in either theoretical or applied physics. Thus, the understanding of inertia opens the possibility of understanding more about the behaviour of objects, thereby optimizing our ability to predict, control, and benefit from such behaviour in a range of fields, while thus the study of inertia remains one of the basic positions in classical mechanics, shaping profoundly our understanding of the real world.

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