Final answer:
Galileo used a water clock to measure the fall time of the objects. He observed that the objects reached the ground at the same time, regardless of their mass. This result would also hold true if the experiment was conducted on the Moon.
Step-by-step explanation:
In Galileo's leaning tower experiment, he dropped two objects of different masses from the Tower of Pisa to demonstrate that, in the absence of air resistance, all objects fall towards the center of the Earth with the same constant acceleration, independent of their mass. Since stopwatches weren't available at that time, Galileo likely used a method called a water clock, where the time is measured by the water flow rate. If the objects were the same size but with different masses, Galileo would have observed that both objects reached the ground at the same time, as their masses do not affect their fall time when air resistance is negligible. On the Moon, this experiment would yield the same result since the acceleration due to gravity is constant regardless of location.