I was talking to my friend about which model to use to describe the "amount" of movement something has.
I said momentum is almost always "better" since it involves direction.

He told me that with space rockets they actually use kinetic energy. I didn't understand his reasoning for this. He said something like
>"with a race car, you have a fixed road underneath the car. with a space ship there's no reference point underneath it - it's like the rocket is constantly on the starting lane. momentum makes no sense in this context"

Try to make sense of what he was getting at, and what I'm not understanding here.