User talk:Thepossumdance

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Your edit to 'De motu ...'
Hallo, Thepossumdance. I'm interested in your edit to 'De motu...'. Have you got a source for saying that Newton gave derivations of Galileo's laws? Didn't Newton just rely on them as part of the background? What leads you to say that he derived them? With good wishes, Terry0051 (talk) 00:00, 8 December 2009 (UTC)
 * Thanks for your message. I think the original sentence that you modified had been about derivations. But which part of the (Newton) description is it that you would say supports this?: "His description as such is enough to say that Galileo's laws are very good approximations but not exact."?  As I read it, Newton (in many places) does something different from that, he assumes Galileo's law that under constant acceleration distance is proportional to time2 -- (I don't suggest that was anything other than a perfectly respectable thing to do, the law was well established) -- and Newton often applies it in a new way to evanescent initial time-increments in order to prove some relationship in the limit.


 * (btw, it would be appreciated if you would add any new sections at the bottom of the talk page rather than the top, and I know that this is the preference of many others on WP too.)


 * With good wishes, Terry0051 (talk) 16:44, 10 December 2009 (UTC)

Thanks for your further message. What seems clear is that you're referring to a Newtonian proof (a) that relates to ellipses (while in contrast a correspondng curve by Galileo would be a parabola) and (b) that is based on a centripetal inverse-square force-law. It would clearly be misleading to call this a mathematical derivation relating to Galileo's laws because it relates to conditions that are specifically not in accordance with Galileo's laws. Terry0051 (talk) 22:27, 10 December 2009 (UTC)

Terry0051 (talk) 16:29, 16 December 2009 (UTC)