A collision's an isolated event in which two or more moving bodies (colliding bodies) exert relatively strong forces on each other for a relatively short time. Dynamics Collisions involve forces (there's a change in velocity). Collisions can be elastic, meaning they conserve energy and momentum, inelastic, meaning they conserve momentum but not energy, or totally inelastic (or plastic), meaning they conserve momentum and the two objects stick together. The magnitude of the velocity difference at… (More on Collision)