Re: Double Your Momentum, Reflection


W. Watson wrote:
> IsaacKuo wrote:
>
> > Charles wrote:
> >
> >>On 7 Dec 2005 12:26:24 -0800, "PD" <TheDraperFamily@xxxxxxxxx> wrote:
> >
> >
> >>>Initially, ball has momentum +P and wall has momentum 0.
> >>>Finally, ball has momentum -P and wall has momentum +2P.
> >>>Total momentum is conserved (+P in both cases).
> >
> >
> >>I managed to confuse myself with your explanation.
> >
> >
> >>Imagine two walls. Let's put them in orbit, so there is no coupling
> >>between them. Elastic ball and walls. so little loss.
> >
> >
> >>the ball hits one wall and results in the momentum as you state. It
> >>bounces to the second wall, regains its +p momentum and imparts -2P
> >>momentum to the second wall. Then it bounces to the first wall again,
> >>which still has its +2P momentum, now it gets 2 more, so it results in
> >>+4P? This can progress for a long time?
> >
> >
> > Yes, in principle it can keep going until the walls are moving outward,
> > each with half of the kinetic energy the ball originally had. As the
> > walls move apart faster and faster, the ball loses more and more
> > velocity with each bounce.
> >
> > Isaac Kuo
> >
> That's certainly interesting.
>
> I guess no mv1+mv2=const is going to work here (original query).
>

Sure it does. You just have to remember that momentum is a *vector*
quantity.
A momentum of mv to the left plus a momentum of mv to the right is a
total momentum of *zero*, not 2mv.

PD

.

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