A Galilean thought experiment

Illustration for article titled A Galilean thought experiment

Find out about a four-hundred-year-old thought experiment that upset the Aristotelian school of thought, which held that heavy objects fell faster than light ones.


Aristotle, one of the great minds of the classical world, is known for being wrong about many things. Many, many things. He was wrong about the number and composition of the elements, the number of legs on a fly, and the speeds of two different falling weights.

Unlike the fly debacle, the falling objects are understandable. Aristotle believed that things fell at a constant speed, not accelerating, and that lighter objects fell more slowly than heavier ones. Since lighter objects tend to be more affected by wind resistance, they fall more slowly. Wind resistance helps determine terminal velocity – the speed at which an object can't fall any faster since the force of air resistance pushing up and the force of gravity pulling down cancel each other out – and slower moving objects are easier to observe. So they are seen falling at a constant rate, more slowly than heavier objects, and the theory is ‘proved'.

Galileo disproved that theory, but not before he baffled, amazed, and probably annoyed the hell out of the people around him with a delicious conundrum. So a heavy object falls quickly. And a light object falls slowly. What happens when a light object is attached - say, with string - to a heavy object?

A light object and a heavy object would obviously make an even heavier object. That heavier mass would then fall faster than either of the original objects.

But wait! The light object falls more slowly than the heavy object. The weight of the string might increase its weight slightly, but it would still fall more slowly than the heavier object. This means that it would be tugging the heavier object up, and the entire mass would fall slower than at least one of the original objects.

It's also possible to prove Aristotle wrong with a vacuum chamber, a feather and a bowling ball, or two differently weighted bowling balls and a great enough height - or, for that matter, with a fly. This thought experiment, however, has the inestimable benefit of being able to the carried out with one's ass firmly glued to a chair and a smug smile firmly glued to one's face. It's much better.


Via Philosophical Investigations.



I've had thought experiments about gravity too. Except in mine, the coyote doesn't fall till he realizes he is falling. I have yet to prove it as I haven't been able to capture a coyote and throw it over a cliff.