## LESSWRONGLW

[anonymous]7y1

And all it takes is to let go of one outdated idea, which is, like Aristotle's impetus, ripe for discarding.

This is not at all important to your point, but the impetus theory of motion was developed by John Philoponus in the 6th century as an attack on Aristotle's own theory of motion. It was part of a broadly Aristotelian programme, but its not something Aristotle developed. Aristotle himself has only traces of a dynamical theory (the theory being attacked by Philoponus is sort of an off-hand remark), and he concerned himself mostly with what we would probably call kinematics. The Aristotelian principle carried through in Philoponus' theory is the principle that motion requires the simultaneous action of a mover, which is false with respect to motion but true with respect to acceleration. In fact, if you replace 'velocity' with 'acceleration' in a certain passage of the Physics, you get F=ma. So we didn't exactly discard Aristotle's (or Philoponus') theory, important precursors as they were to the idea of inertia.

In fact, if you replace 'velocity' with 'acceleration' in a certain passage of the Physics, you get F=ma.

That kind of replacement seems like a serious type error - velocity is not really anything like acceleration. Like saying that if you replace P with zero, you can prove P = NP.

# 27

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