Hi guys. I just got a general question. 1. The problem statement, all variables and given/known data 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. 2. Relevant equations So if momentum is conserved, why there is a change in momentum? 3. The attempt at a solution I am so confused. I will appreciate your help!