Talk:De motu corporum in gyrum

message: Newton told Halley that he had proved that the inverse-square force necessarily resulted in an elliptical orbit. (Can't find it right now. I'll send it to you later.) Instead of this proof, Newton sent De Motu to Halley. This treatise contained a demonstration of how an elliptical orbit can be related to the inverse-square force. This was the opposite of what was promised.Lestrade 14:36, 4 February 2006 (UTC)
thread_title: Not That There's Anything Wrong With That

message: How did Newton know that all of the planets move at the same speed and also know what that speed was? How did he know that a comet moves faster than a planet? Does today's science agree with Newton's pronouncements about the speeds of planets and comets?Lestrade (talk) 18:20, 11 April 2008 (UTC)
replies: text: According to Newton, the ellipticity of a planet's orbit depends on its speed. Wikipedia shows the orbital speeds of the planets are as follows, in kilometers per second: Mercury 48, Venus 35, Earth 30, Mars 24, Jupiter 13, Saturn 10, Uranus 7, Neptune 5, Pluto 4.6. If Newton was right, then the planets should all have differently shaped orbits. Pluto, the slowest, would be the most circular. Mercury, the fastest, would be the most elliptic, almost parabolic. Is this true?Lestrade (talk) 17:42, 29 April 2008 (UTC)
thread_title: Orbital speed

message: It's only a few pages long. It was the basis of the most important scientific book ever written. Then why is it almost impossible to find De motu in print? Could it be that Newton's idiosyncratic geometry is so unreadable that it might as well have been written by Professor Irwin Corey?Lestrade (talk) 21:19, 11 April 2008 (UTC)
replies: text: Yeah, I'm doing a project on him and I can't find it.  whatn is wi6th that.  Please replyTailsfan2 (talk) 17:32, 21 October 2008 (UTC)
thread_title: Funny footer

message: There's a law missing:
Law 3 is actually what became Newton's 3rd law (equal and opposite reaction), and Laws 3-5 listed on this page should all be shifted down one.  —Preceding unsigned comment added by 128.12.93.134 (talk) 11:12, 9 June 2009 (UTC)
thread_title:  Missing Law 

message: A question has been raised about whether Newton gave mathematical demonstration of Galileo's laws.  It looks as if Newton used and built on Galileo's results rather than as if he proved them (for the restricted conditions in which they are valid).  
There is no mention of Galileo (as far as I can see) in the first version of Newton's 'De motu' (links to cited sources are already in the main article text).  On the other hand, Newton did later acknowledge Galileo in connection with the first two laws of motion when he expanded the 1684 'De motu' and produced the 'Principia' of 1687 (Scholium to Corollary 6, at page 31 in the 1729 translation. At that point Newton credited Galileo with the discovery that the descent of bodies (under practically constant force) was proportional to the square of the time, and Newton also credited Galileo with making that discovery by using the relationships that Newton had just set out in the first two laws of motion and their first two corollaries (for which, see pages 19 to 24 in the 'Principia', 1729 translation).
In 'De motu', Newton applied the proportionality between distance and square of the time for infinitesimal use, and he stated application that as his fourth 'hypothesis' in the 1684 'De motu' (compare Lemma 10 in the 'Principia'). (btw, it looks as if Newton in 1684 was using the term 'hypothesis' to mean something like 'starting-point', according to its etymology, and not to mean something conjectural or uncertain. That seems to emerge especially because in the passage cited above from the Scholium to Corollary 6, Newton writes that he has been discussing things that "have been receiv'd by Mathematicians and are confirm'd by abundance of experiments".  Clearly he was not talking about guesses or speculations.)
It doesn't look as if any source has been mentioned that points to a proof by Newton of Galileo's laws, as opposed to the sources that show Newton appearing to use the acknowledged prior results of Galileo rather than to prove them. Terry0051 (talk) 16:28, 16 December 2009 (UTC)
thread_title:  Newton and Galileo 

message: This item appears on the Wiki "this day in history" page for 10 December, but that's a Gregorian calendar and this event took place on 20 December 1684, 10 December O.S. I presume that everyone involved in this page knew that, or knew that it needed to be calculated, but I see no reference to the calendar issue here so I don't want to change it.Vanhorn (talk) 08:22, 10 December 2011 (UTC)
thread_title: Date