# Law of Inertia

LAW OF INERTIA

Law of inertia, also known as Newton’s first law of motion, states that

An object will continue to be in the state of rest or in a state of motion unless an external force acts on it.

### INERTIA

The inherent attribute of all the bodies, by virtue of which they oppose the change in the state of rest or of uniform motion along the straight line on their own, is called inertia.

Some real-life applications to describe the inertia are as follows:

• Tables and chairs are kept inside the classroom and remain in a state of rest until someone moves them.

The reverse can also be true.

• Suppose I am driving a car at a high speed. Suddenly, I encountered a big rock. I need to apply force to stop the car to bring it to a state of rest.

GALILEO EXPLAIN INERTIA

The concept of inertia was created by Galileo, a leading scientist in the seventeenth century. According to Galileo, moving objects eventually come to a standstill due to a force known as friction. Galileo found that a falling object gains an equal amount of velocity in equal intervals of time. This also means that the speed increases at a constant rate as it falls. But, there was a problem in testing this hypothesis: it was impossible for Galileo to observe the object’s free-falling motion and at the time, technology was unable to record such high speeds. As a result, Galileo attempted to decelerate its motion by replacing the falling object with a ball rolling down an inclined plane. Since free-falling is basically equivalent to a completely vertical ramp, he assumed that a ball rolling down a ramp would speed up in the exact same way as a falling ball would.

Using a water clock, Galileo measured the time it took for the rolling ball to reach a known distance down the inclined plane. After several trials, it was observed that the time it took for the ball to roll the entire length of the ramp was equal to double the amount of time it took for the same ball to only roll a quarter of the distance. In short, if you were to double the amount of distance the ball travelled, it would travel four times as far. Through this experiment, Galileo concluded that

If an object is released from rest and gains speed at a steady rate (as it would in free fall or when rolling down an inclined plane), then the total distance travelled by the object is proportional to the time squared needed for that travel.

Some examples of the Law of Inertia

• The lift began abruptly.
• When a stationary bus begins to move, it has a tendency to move backwards.
• When the lift suddenly operates, it causes a jerk.
• When an abrupt break is applied, you can go forward.

## TYPES OF INERTIA

• Inertia of Rest: -

When the resistance is offered by the body to continue in the state of rest unless an external force acts on it.

• Inertia of Direction: -

When the resistance is offered by the body to continue the motion in the same direction unless an external force acts on it.

• Inertia of Motion: -

When the resistance is offered by the body to continue to be in the uniform motion unless an external force acts on it.

SOME EXAMPLES OF LAW OF INERTIA OF REST IN OUR DAILY LIFE

When a bus or a train starts suddenly, the passenger standing inside it falls backward: It happens because the feet of the passenger being in contact with the floor of the bus come in motion along with the bus but the upper part of the body remains at rest due to inertia of rest. Hence the passenger falls backward.

SOME EXAMPLES OF LAW OF INERTIA OF DIRECTION IN OUR DAILY LIFE

• The water particles sticking to the cycle tire are found to fly off tangentially whenever a driver is negotiating a curve; the passengers experience a force acting away from the centre of the curve.
• When a bus driver is negotiating a curve on the road, passengers fall towards the centre of the curved road. Whenever a driver is negotiating a curve, the passengers experience a force acting away from the centre of the curve; it happens due to the tendency of the passengers to continue moving in a straight line.

SOME EXAMPLES OF LAW OF INERTIA OF MOTION IN OUR DAILY LIFE

If you are on a train and the train is moving at a constant speed, a toy tossed into the air will go straight up and then come down. This is because the toy has inertia like the train and you.

• Luggage is usually tied with a rope on the roof of a bus. When the bus stops suddenly, the luggage kept on the roof may fall from the roof of the bus due to inertia of motion therefore, it is advised to tie any luggage kept on the roof of a bus with a rope.