If you have both a basketball and a tennis ball, try dropping the two of them onto a floor with a hard surface, first individually and then with the tennis ball placed on top of the basketball before the two are dropped together.
a. Compare the height of the bounce of each ball in these different cases. The case where the two are dropped together may surprise you. 

b. Can you devise an explanation for these results using impulse and Newton’s third law? (Consider the force between the basketball and the floor as well as that between the tennis ball and the basketball for the case where they are dropped together.)