Originally Posted By: paul

Nope, that is not what we are saying. What we are saying is when you move either one of those you get equal forces in both directions.

just what are you saying bryan?
once again I ask...

1) do you think the pipe will move.

if you think the pipe will move , given that the pipe moves
due to a constant force.

2) do you think the pipe will suddenly stop.

Answer to 1 depends on what you mean by "move". The pipe will move relative to the mass moving inside of it. The center of mass of the whole system - i.e. pipe + mass - will not move, as observed by an outside observer. In other words, the individual parts will move, but the whole will not.

As for 2, the answer is yes. When the ball hits the end of the pipe, or is turned around, or is otherwise braked, it will exert a force equal to the force that started it moving in the first place. That force will stop the movement of the pipe.

On the other hand, if your pipe were open, so the ball could freely exit into space, than the pipe would continue in its movement unabated, and thus you would have achieved a net change in the momentum of the pipe. I'd point out that is the very essence of how a rocket works.

Originally Posted By: paul
I dont even know why I bother trying to get a straight answer from you two clowns.

Probably because deep down inside you realize we're right.