Imagine two balls, one heavier than the other, connected by a string. Drop this system of objects from the top of a tower. If we assume heavier objects do indeed fall faster than lighter ones (and conversely, lighter objects fall slower), the string will soon pull taut as the lighter ball drags on and slows the fall of the heavier ball. But the system considered as a whole is heavier than the heavy ball alone, and therefore should fall faster than the heavy ball on its own. So Aristotle’s theory, just like the claim that there exists a four-sided triangle, generates a contradiction. Galileo could establish that it is false from the comfort of his armchair.Quite. Philosophers have always preferred the comfort of armchairs and a good book, perhaps scientists should try this too. And following up Belette's question about Buridan's theory of impetus, I looked this up too. Buridan (in the twelfth question of Subtilissimae Quaestiones super octo Physicorum libros Aristotelis) challenges Aristotle's theory of why, when we throw an object through the air, it does not come to an abrupt halt and does not come crashing to the ground, as Aristotle's theory says it should. Aristotle's daft explanation is that the air projected by the thrower somehow propels the object forward. Buridan puts forward a number of armchair objections to this, of which the nicest involves the motion of a millwheel. This keeps turning in a circle once put in motion, yet circular motion does not displace any air. And this was even before the invention of armchairs (although admittedly you would have had to have seen a millwheel in operation to make this argument, and thus armchairs while necessary are not sufficient).
I would love this to be in the Logic Museum but the only edition I can find is from 1509, and early printed books are generally resistant to scanning. Something for the summer break, perhaps.