Re: [Phys-l] Rocket Hovering and Conservation of Momentum

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

The change in momentum of the gas after it leaves the rocket cannot, at 
leasst in first order, have any effect on the rocket.  I don't understand 
your remark after the "but".
			Regards,
				Jack



On Mon, 24 Jul 2006, Marc "Zeke" Kossover wrote:

> --- Jack Uretsky <jlu@hep.anl.gov> wrote:
>
> > The answer to
> > what is getting
> > upward momentum is, simply, the earth.  The added
> > downward momentum from
> > the gas is from the gravitational attraction of the
> > each.
>
> This is what I originally thought (and the student, too)
> but it leaves out the fact that the rocket does get some
> positive momentum as well. The rocket end up upwards from
> it's original position, even though it remains the same
> distance from the planet.
>
> >  	I advocate keeping it simple and accompanying the
> > answer with a
> > diagram showing the gas, the earth, the mutual forces
> > acting on each, and
> > nothing else.
>
> Sure, but he was wondering about momentum conservation. And
> I think that he was leading me towards asking the more
> vexing question about momentum conservation in a plane with
> level flight.
>
> Marc "Zeke" Kossover
>
>
>
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