# Why does impulse exist?

Hi guys. I just got a general question.

## Homework Statement

I learned about impulse today in class, and I just wonder why it exists?

Impulse is defined as "the change in momentum", but momentum is always conserved in elastic collision.

## Homework Equations

So if momentum is conserved, why there is a change in momentum?

## The Attempt at a Solution

I am so confused. I will appreciate your help!

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