…though in this case, “the hammer” is a bowling ball. In this excellent clip from the BBC’s Human Universe: Episode 4, Professor Brian Cox visits NASA’s Space Power Facility in Ohio, home of the world’s biggest vacuum chamber, to test Galileo Galilei‘s Leaning Tower of Pisa experiment, circa 1589:

If you drop a brick and a feather at the same time the brick will probably hit the ground first. But this is because of differences in the amount of friction between these objects and the air around them, not because their masses are different. If there were no air…

What happens? How does a hammer, brick, or bowling ball move in comparison to the feathers when you remove any air resistance? Watch.

via io9.