Hmm, have you read Aristotle? So far as I can tell, his most extended argument on the matter is Physics VI.8, where he argues that in an atmosphere, heavier things fall faster because they are better able to divide the medium owing to greater downward force. He then argues that in a void, heavier and lighter things would fall with the same speed. Since this is not what we observe (we do in fact often observe heavier things falling faster for the reason Aristotle cites) there cannot be any void.
Do you mean Physics IV.8 ? There he asserts that velocity = (weight / density). The argument that there cannot be any void is that you cannot divide by zero—in modern terms, the velocity of the falling objects would approach infinity as density approaches zero.
Galileo established that this equation greatly overestimates the density of water when compared to experimental results. Also, Aristotle’s equation would suggest that a brick would fall twice as fast as half of a brick, which would have been easy to test; sadly, while Aristotle was one of the best empiricists of his time, he still didn’t think of actually looking.
I did, I edited it but not in time. Thanks for the catch.
Your description of Aristotle’s argument proceeding the one I cited seems accurate to me, though it doesn’t seem to me that Aristotle took the correctness of his ratio to be important: he doesn’t bring it up again, and a different ratio would have produced the same result so far as his argument went. So...
Also, Aristotle’s equation would suggest that a brick would fall twice as fast as half of a brick, which would have been easy to test; sadly, while Aristotle was one of the best empiricists of his time, he still didn’t think of actually looking.
Why look? His point is that the difference in fall-rates of heaver and lighter objects is due to a ratio of downward force against atmospheric resistance. That’s roughly right. The ratio itself doesn’t matter, if the point is just to argue against motion in a void. As a matter of understanding Aristotle’s physics, it’s important to understand that he didn’t really care about mechanics. His physics is about a different subject matter.
The argument I described to Anubhav follows the one you cite. I’ll quote it here:
“These are the consequences that result from a difference in the media; the following depend upon an excess of one moving body over another. We see that bodies which have a greater impulse either of weight or of lightness, if they are alike in other respects, move faster over an equal space, and in the ratio which their magnitudes bear to each other. Therefore they will also move through the void with this ratio of speed. But that is impossible; for why should one move faster? (In moving through plena it must be so; for the greater divides them faster by its force. For a moving thing cleaves the medium either by its shape, or by the impulse which the body that is carried along or is projected possesses.) Therefore all will possess equal velocity. But this is impossible.”
The point here isn’t that Aristotle was right. We can just point to any aspect of astrophysics to see that he wasn’t. The point is just that we tend to attribute to Aristotle a lot of views that he didn’t hold, and about matters that weren’t important to his overall project.
Do you mean Physics IV.8 ? There he asserts that velocity = (weight / density). The argument that there cannot be any void is that you cannot divide by zero—in modern terms, the velocity of the falling objects would approach infinity as density approaches zero.
Galileo established that this equation greatly overestimates the density of water when compared to experimental results. Also, Aristotle’s equation would suggest that a brick would fall twice as fast as half of a brick, which would have been easy to test; sadly, while Aristotle was one of the best empiricists of his time, he still didn’t think of actually looking.
I did, I edited it but not in time. Thanks for the catch.
Your description of Aristotle’s argument proceeding the one I cited seems accurate to me, though it doesn’t seem to me that Aristotle took the correctness of his ratio to be important: he doesn’t bring it up again, and a different ratio would have produced the same result so far as his argument went. So...
Why look? His point is that the difference in fall-rates of heaver and lighter objects is due to a ratio of downward force against atmospheric resistance. That’s roughly right. The ratio itself doesn’t matter, if the point is just to argue against motion in a void. As a matter of understanding Aristotle’s physics, it’s important to understand that he didn’t really care about mechanics. His physics is about a different subject matter.
The argument I described to Anubhav follows the one you cite. I’ll quote it here:
The point here isn’t that Aristotle was right. We can just point to any aspect of astrophysics to see that he wasn’t. The point is just that we tend to attribute to Aristotle a lot of views that he didn’t hold, and about matters that weren’t important to his overall project.