Reading Questions: Philoponus on Free Fall
(Questions for reflection, which cannot necessarily be answered simply by reading the text but should be provoked by it, are marked with an asterisk.)
John Philoponus, Commentary on Aristotle's Physics, pp. 678.24 - 684.10 (Vitelli)
1. Subject to some important restrictions, Aristotle's views on free fall can be summed up by the equation
V = F/R
where V is the velocity, F is the force (weight, as both Aristotle and Philoponus would have agreed), and R the resistance of the medium. (Aristotle never gives this equation as such. We could express what he actually says more faithfully as a statement of proportionality, but we can turn this into an equation by choosing our units judiciously. For ease of discussion we may as well assume that this has been done and stick with the equation.) How does Philoponus make it clear that he is opposed to this analysis of free fall? Cite a couple of specific lines.
2. Philoponus offers a different interpretation of the situation that can be summed up in a different equation that links the same variables. What is it? Cite textual support for your alternative equation.
3. What claim of Aristotle's does Philoponus say he has undermined? Explain why this is so in terms of your reconstruction of his equation for motion.
4. Philoponus goes on to argue that Aristotle is wrong to say that, if there were a void, and a body could move through it with a finite velocity, then some body would move through both the void and a plenum (perhaps a suitably, but not infinitely rarefied one) at the same rate of speed. (a) Reconstruct Aristotle's argument for this, taking for granted his equation linking V, F, and R. (b) Show that the substitution of Philoponus's equation for Aristotle's would lead to Philoponus's result.
5. What, approximately, is a stade? (You may want to check Danielson, p. 48)
6. What consequence regarding the free fall of two bodies of different weight does Philoponus deduce from Aristotle's views?
7. In a very famous passage Philoponus describes an experiment to test this. What does he say the outcome is? (Be precise.)
8. What is Philoponus's final conclusion? Derive it from his equation linking V, F, and R.