Inertia

The tendency of an object to resist changes to its state of motion.

What is Inertia ?

This property of the body to continue in its state of rest or uniform motion unless acted upon by a net external force 'or' the inability of a body to change its state unless acted upon by a net external force 'is known as inertia.

Types of Inertia

based on the state of the body, inertia is classified as follows: Inertia of Rest: It is the resistance of the body to change its state of  rest or of motion. Example: (a) When books are piled one above the other and the lowest book is suddenly pulled out, the rest of the books remain intact. This is due to inertia of rest. (b) When the bus starts suddenly, the standing passengers in the bus tend to fall backward. When the bus is at rest, the entire body of a passenger is at rest but when the bus starts suddenly, the lower part of the body of passenger which is in contact with the bus moves along with the bus while the upper part remains at rest  due to inertia of rest.  Hence, the standing passengers tend to fall backwards. Inertia of Motion: If a body is in a state of uniform motion, it continues to remain in the same state unless an external force acts on it. Example: (a) When a boy who is running is tripped by a stone, he falls, because his feet come to rest whereas the upper part of his body continues to move forward due to inertia of motion. (b) A passenger standing in a moving bus tends to fall forward when the driver of the bus suddenly applies the brakes, this is because the feet of the passenger (which are in contact with the bus) come to rest along with the bus  but the upper part of his / her body continues to move forward due to inertia of motion. Inertia of Direction: It is the inability of a body to change its direction of motion on its own. Examples: When a car takes a sudden turn towards the left, the person seated inside it is pushed toward the right. This as because when the car takes a sharp turn it changes its direction whereas the person seated inside tends to move in the original direction due to inertia. Hence, he is pushed towards the right.

Mass and Inertia

If a football is kicked, it moves a long way.  But if an iron ball of the same size is kicked with the same force it hardly moves. This implies that the iron ball has more inertia than a football. Similarly, a greater force is required to stop a loaded truck than an empty one. Hence, a truck loaded with bricks has more inertia than an empty truck. Thus, a heavier body has more inertia than a lighter body.  All objects do not offer the same resistance to change their state of rest or of uniform motion. Thus, we may conclude that the mass of a body is the measure of its inertia.

Difference between mass and inertia

Inertia - The tendency of an object to resist changes to its state of motion. Mass - The measure of inertia of a body is called mass.

Examples of inertia in daily life

1. When paddle is stopped while riding a bicycle, the bicycle rolls far.  
2. Passengers are bent forward when a bus or train stops suddenly.  
3. Passengers are bent backwards when a bus or train is suddenly moved.