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

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Comments

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. :)

Mursalin Habib - 7 years, 9 months ago

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

Tamoghna Banerjee - 7 years, 9 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$