On a Philosophy Bites podcast I heard Daniel Dennett mention the following

On a Philosophy Bites podcast I heard Daniel Dennett mention the following thought experiment, which he attributed to Galileo. Suppose that heavier objects fall faster than light ones. Take two objects, A and B, where A is lighter than B. Connect A and B with a string and drop them. Since A is lighter than B, A will act as a drag on B, and B will fall more slowly than it would have alone. Yet since A and B are jointly heavier than B, and heavier objects fall faster than light ones, B will fall faster than it would have alone. We have a contradiction. Therefore, heavier objects do not fall faster than light ones. I thought that this was really marvelous and also very surprising. I had been under the impression that one could not arrive at ostensibly substantive empirical claims like the one in question just by considering thought experiments. I was hoping that one of the panelists could explain exactly how Galileo's thought experiment works here.

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