Re: Conservation of momentum (and a weird space drive)

From: Joe (jhelfand_at_umd.edu)
Date: 10/10/04 

Date: 10 Oct 2004 13:49:40 -0700

Tom,

> Yes. That's why I started and ended with everything (m and carrying
> mechanism) in the same state (position) on the planet. That means M and
> m end up in their initial positions in that inertial frame.
>
> Have your canoeists throw the ball a second time so it is back where it
> started relative to the canoe, and the canoe and canoeists and ball move
> back to where they started (in the water). I'm neglecting friction and
> other minor effects here.

You're ofcourse right, I misread what you wrote. But what I still
don't get is how the light "accelerates" the planet upwards to meet
the photon? How does the extra kick from the photon get ballanced?
Never mind carrying the flashlight up and down, I can see (probably
naively) that this doesn't impart a net motion in any direction. But
what I'm confused about, is the light striking the surface. You can
quote that momentum is conserved in a closed system, but at least in
Newtonian Mechanics there's a reason for that, in that there are equal
and opposite forces. Does that mean that as the momentum falls, and
increases momentum, there is a corresponding increse in the momentum
of the planet in the opposite direction? Doesn't this violate no
"action" faster than light?

Relevant Pages

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