# Why do we say that force is directly proportional to change in momentum?

Any examples??

### 5 Answers

- 8 years agoFavorite Answer
That is the definition of force. And remember momentum is always conserved.

- Lola FLv 78 years ago
We do not say that force is "directly proportional" to change in momentum. We define it to be *exactly equal* to change in momentum. We define it to be that way because momentum is conserved, and keeping track of changes in the momentum of one body is the way to determine changes in others.

- Andrew SmithLv 78 years ago
Impulse = change in momentum

F * t = m * (change in v)

to see why, divide both sides by t

F = m * (change in v) /t

But change in v / t = acceleration.

hence F = ma which is the very definition of force.

Now back to the formula at the top.

If the time of the collision is kept constant, then doubling the momentum doubles the force

and so on.

It is proportional because

F2/F1 = (mv)2/(mv)1

for any values of F or mv as long as we keep the time a constant.

- 8 years ago
Because, Change in momentum of a body of a constant mass, is proprtional to change of velocity. The rate of change of velocity is acceleration. Since force = MassxAcceleration, it is proportional to rate of change of momentum.

No examples! It is obvious..Think over it!

Hope it helped

- How do you think about the answers? You can sign in to vote the answer.
- 203Lv 78 years ago
We say it because it is a demonstrable law of physics.

Example, every moving object in existence