Re: [Phys-l] Rocket Science

[Jack Uretsky <jlu@hep.anl.gov>]

Hi Carl-
	If you had equations for r(t) and \phi (t), could you get an 
equation for r(\phi )?  Would that answer your question?
					Regards,
						Jack

On Fri, 28 Jul 2006, Carl Mungan wrote:

> >   -- Make sure all orbits are closed
>
> Oh good, that's exactly a question I had about a different problem. I seem to recall reading in mechanics books that only the inverse square and harmonic oscillator force laws give rise to closed orbits.
>
> But how does one prove in general that orbits are closed in a given problem? Suppose either you are given differential equations for r(t) and phi(t), which one should probably be able to translate into a second-order equation for r(phi), or equivalently say you are given the force expression and relevant conservation laws? -Carl
>
>
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