Out of the mouth of babes....
In this case I'm strictly referring to the post title... "high school physics".
Well done, Bryce!
Go and stand on a skateboard with a bag of sand.
Throw it backwards, and you'll move forwards. Rocket engine.
Now stand on your skateboard and have somebody throw a bag of sand towards you. Catch it and you'll move backwards. Put your own energy into it and throw it backwards faster than it arrived. You'll move forwards. Jet engine.
CJ