Question

Explain the differences between inertia of motion and inertia of rest.

Answer 1

Hint: Inertia of motion and inertia of rest both obeys Newton’s first of motion. In inertia of motion, the body must be in motion and must be in uniform motion whereas in inertia of rest, the body must be in state of rest. If net external force on a body is zero, its acceleration must be zero.

Completes step by step solution:
When it comes to Law of Motion, Law of Inertia the most important point. The state of rest or uniform linear motion both imply zero acceleration. First law of motion can therefore be simply expressed, “if the net external force on a body is zero its acceleration is zero. Acceleration can be non-zero only if there is net external force on the body”. Two kinds of situations are encountered in the application of this law in practice. In some examples we know that the net external force on the object is zero. In that case we can conclude that the acceleration of the object is zero. For example a spaceship out in interstellar space, far from all other objects and with all its rockets turned off, has no net force acting on it. Its acceleration, according to first law, must be zero. If it is in motion it must continue to move with a uniform velocity. And more often however we do not know all the forces to begin with in that case if we know that an object is accelerated , that is it is either at rest or in uniform linear motion we can infer from first law that the net external force on the object must be zero gravity is everywhere.
Some examples of inertia of rest: book placing on table. Book will not move until and unless external force will act on it. But if we move the table then the table will move and the book will be in motion but actually it is in the body. It is a table which is moving.
Some examples of inertia of motion: passengers in a bus who are standing experience force. Car will always be in motion if the driver does not apply the brakes.

Note: Every body continues to be in rest or of uniform motion in a straight line unless compelled by some external force to act otherwise. If the body is under gravitation, the gravitational force is the one which will act on the body.