Originally Posted By: paul
I only consider that the mass gains momentum as it is pushed down the accelerator.

When I say "gains momentum" I mean "momentum becomes more positive". I'll try to use that wording from now on.


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what does the sentence below mean to you?

The pipe has momentum -1

knowing that a momentum of -1 would be saying that the pipe is moving in the negative direction with a magnatude of 1

Yes.

Quote:

are you saying that the pipe would not stop after the 1st turn?

Yes

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so if you are trying to say that the pipe will go from a +1 momentum to a -1 momentum

Yes




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what is happening in the 1st turn is that as the mass pipe
...
transfers the other 1/2 of its momentum force to the mass.

Be precise. There's no such thing as "momentum force". This kind of detail is why we're having so much trouble communicating.



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because it started with 2 units of momentum only in different directions and because the pipe is moving towards the mass the pipe may accelerate the mass even further as the pipe stops.

No no, absolutely not. Momentum is a vector. So when you add momentums you have to do vector addition. In 1D that means -1 + +1 = 0. It does not mean |-1| + |+1| = 2. No way.

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How about apply conservation of energy. There's no way you can doubt it's applicability to a simple 1D elastic collision, which is what we have.

You say:

Before the 1st turn
the mass has kinetic energy X
the pipe has kinetic energy Y > 0
Total kinetic energy = X+Y

After the 1st turn
the mass has kinetic energy X
the pipe has kinetic energy 0
Total kinetic energy = X

Kinetic energy has been reduced by Y. We have no friction or other energy loss. So this is impossible.