Hello students, in this article we are going to discuss the term called as Inertia. Just try to think upon the questions, why objects are not able to change its state from rest to motion or vice versa by its own? Bullet fired from the gun always travels in straight line? Blades of ceiling fan continue to rotate even after switching of the electric circuit, why? The answer for all of these questions is ‘Inertia’.
We know that every substance posses mass, due to which it has heaviness. This heaviness leads to term known as inertia. Inertia opposes any kind changes in state of body. Hence inertia is defined as ‘the tendency of body to resist the change of state of body.’ Force changes the state of object by overcoming its inertia.
Inertia of a body can be categorised as,
1.) Inertia at rest:
The tendency of body to resist change in its state of rest is termed as inertia of rest. Until and unless external force acts on body, its state cannot be changed. Applied force overcomes the heaviness by cancelling its inertia.
For all objects the quantity mass provides the inertia when it is at rest. Due to presence of gravitational force the very body posses its own force i.e. weight. So that we have to overcome the weight by applying the external force which should be greater than weight of body so that the body can change its state from rest to motion.
Eg. A stone at the peak of mountains doesn’t falls down unless somebody pushes it with large force.
2.) Inertia of motion:
The tendency of body to resist change of its state of motion is termed as inertia of motion. External force is required to change the state of from motion to rest.
When object is in motion, along with mass, velocity also contributes inertia. Here the product of mass and velocity i.e. momentum provides the inertia. So stop the moving object we have to change momentum of the object. To stop running car, we need to apply brakes so that the momentum of car is opposed by brakes and car slows down. Running fan doesn’t stops immediately after switching it off, its due to the momentum of fan cannot be completely resist by frictional force caused by air, so that fan continues to rotates , until and unless its momentums becomes zero.
Eg. Rotation of blades of fan for some instant even though it is switched off, cycle in motion will not stop immediately even if we stop pedalling.
3.) Inertia of unidirection:
The tendency of body to resist change of its direction is termed as inertia of unidirection. Object in motion always continues to travel in straight line since the momentum is always acts along the direction of applied force. So that the path of object becomes straight line and its direction remains same throughout the motion unless any obstacle or external force changes the direction of the body.
Eg. Bullets fired from gun travels in straight line, arrow thrown with help of bow are examples of inertia of unidirection.