Book: #  2

This film is a partial realization of an experiment described by Sagredo in Galileo's Two New Science. 

In the film a ball is dropped three times; the slow-motion factor is seven. 

Scene 1: The ball is dropped by a sailor from the mast. As in Galileo's discussion, the ball continues to move horizontally with the boats velocity, and it falls vertically. 

Scene 2: The ball is tipped off a stationary support as the boat goes by. It has no forward velocity. 

Scene 3: The sailor picks up the ball and holds it briefly before releasing it. The ship and earth are frames of reference in constant relative motion.

Each of the three events can be described as viewed in either frame of reference. The laws of motion apply for all six descriptions. The fact that the laws of motion work for both frames of reference, one moving at constant velocity with respect to the other, is what is meant by Galilean relativity.