Question

Why is it harder to set an object in motion than to keep it moving?

Answer 1

It is harder to set an object in motion than to keep it moving because while in motion, the object has inertia of motion, whereas to set it into motion, we have to overcome its inertia of rest.

• Inertia is defined as:

   The tendency of a body to remain in its state of rest or motion in a     particular direction. Any body having inertia resists a change in its present state.

• As given in the question, let us first consider the case of object at rest. At that moment, the body has inertia of rest and will resist a change in its momentum ( p = m × v , where p is momentum, m is mass and v is velocity). Friction will also have to be overcome by providing energy.

• Now once the object is in motion, it has inertia of motion, therefore it will resist change from motion to rest and hence, it is easier to keep it in motion.

• Other examples of inertia of motion include passengers moving forward when a moving bus stops, liquid continuing to swirl for a while after one has stopped stirring it and so on.