Generally, collisions can be described as either elastic or inelastic. And it's going to be important to figure out which kind you're dealing with, because the math works in very different ways.

Inelastic demand is a term used to describe the unchanging quantity of a good or service when its price changes.

Physicists recognize two distinct types of collisions: “elastic” and “inelastic.” They have technical definitions, but we won’t go too far wrong if we think of an elastic collision as ...