# is it necessary to keep body in motion by applying ext. force

Note by Abhimanyu Manu
4 years, 10 months ago

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In a word- no.

If something is moving and if it is undisturbed, it'll keep moving at a uniform speed in a straight line forever. No force is required to maintain motion.

However this statement is pretty much impossible to verify experimentally. Try to roll a pen on a table. It will eventually stop moving. Why? Because it is not undisturbed. It is rubbing against the table. This rubbing introduces a force on the pen - friction. Friction acts in the opposite direction of motion, slows the pen down and eventually makes it halt.

If you could have a frictionless table surface, the pen would keep moving in a straight line forever. You wouldn't need to apply force on it to keep it in motion (you could apply force on it; that would cause the pen to speed up).

Hope this helps!

EDIT: I just re-read your question. And now I'm confused. Is your question: 'Is it necessary to keep a body in motion?' or 'Is it necessary to apply force to keep a body in motion?' ? I have answered the latter.

If you want the answer to the former question, I'd say: no. If you want to keep a body in motion, keep it in motion. If you don't then don't. It is not necessary to keep a body in motion. :)

- 4 years, 10 months ago

It of course depends on the body's former state.

- 4 years, 10 months ago