# Question on gravitation law derivation

by Thiafon
Tags: derivation, gravitation
 P: 2 Hi, guys. I was wondering on Newton's Gravity Law derivation, and I found this page: http://www.relativitycalculator.com/...vity_Law.shtml Everything seems clear, but the first step is just killing me, because I can't get it. Assuming small incremental changes in s; $$\lim_{t\rightarrow 0} {s} \rightarrow 0$$ we have the following ratios $\frac{\omega}{\nu}$=$\frac{s}{r}$, and $\frac{t}{T}$=$\frac{s}{2πr}$ Could someone help me out? Explain, or just say, which part of math do I have to cover in order to understand that? (btw, I did pre-calculus, and calculus, so concept of limits is familiar to me) Thanks in advance.
 PF Patron P: 10,399 It's just telling you the ratios of everything. The vector changes at the same rate that the distance traveled does since v and r are equal. If you double w you double s as well. In the 2nd ratio, T is the total time of one orbital period and 2*Pi*R is the total distance of the orbit. As t changes, which is the time it takes to transverse the incremental time period s, s changes as well. If you double t you double s. Does that make sense?
 P: 2 Yes, thank you a lot! I had kind of intuitive feeling about it, but I wasn't sure if it is correct.

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