This question is from Resnick, Halliday, Krane; Physics 5th edition. This is not actually a homework problem rather a question and so I hope it's not inappropriate to post it here. If m is a light stone and M is a heavy one, according to Aristotle M should fall fall faster than m. Galileo attempted to show that Aristotle's belief was logically inconsistent by the following argument: Tie m and M together to form a double stone. Then, in falling, m should retard M, because it tends to fall more slowly, and the combination would fall faster than m but more slowly than M; but according to Aristotle the double body (M + m) is heavier than M and, hence, should fall faster than M. What's wrong with this reasoning? If nothing then (in order to prove Aristotle wrong) what need is there for experiment?