Question

what does the law of conservation of momentum say?

Answer 1

@KingGeorge

Answer 2

Energy can neither be created nor be destroyed but it can be transfered from one form to another form. The total amount of energy in the universe remains the same.

Answer 3

That is the law of conservation of energy. Conservation of momentum means that linear or angular momentum is always conserved (i.e., the same before and after).