Leo Galley wants to duplicate the famous experiment in which Galileo dropped two iron balls of unequal weight from the Leaning Tower of Pisa to verify that they fall at the same rate. You can check this for yourself at Galileo Drops the Ball

Leo has nine balls, all of the same size. Even though they all looked alike, he knows one of them is heavier than the rest. He wants to take the heavier one, along with one of the others, up to the top of the Leaning Tower of Pisa and drop them both off.

He has a balance with which to weigh them against each other.

What is the smallest number of weighings he needs to find the heavy ball?

A variation on this month’s puzzle may be found in My Best Mathematical and Logic Puzzles by Martin Gardner.

Try it yourself before looking at our solution