Final answer:
The difference in a collision between two balls and a ball colliding with the floor lies in the impulse due to the various interactions and forces at play.
Step-by-step explanation:
When comparing the collision between two balls and a ball colliding with the floor, the variable that is different in these two cases is the impulse. While the mass, velocity, and change in momentum can be similar, the impulse, which is the change in momentum, might differ because of the different interactions and forces involved in each situation. The floor, being more massive, has a very small change in velocity, but the same change in momentum as the ball due to Newton's third law.