Originally Posted By: paul
Quote:
Do you agree with 4 now after this clarification?

no, because for this discussion the mass is never stopped.


We'll never get anywhere without proper adding of momentum.

Consider another system:
2 identical coins sliding towards each other on a frictionless table top.
Coin 1 has momentum of 1Ns
Coin 2 has momentum of -1Ns


The total momentum of the system is the sum of the two momentums: 1 + -1 = 0

Then the collide and bounce off with some loss.
The total momenum of the system is the sum of the two momentums: -0.5 + 0.5 = 0

Starting again, they collide and both stick together because they have glue on their edges.
The total mometnum of the system is the sum of the two momentums: 0 + 0 = 0

Whatever happens, the total momentum is always 0 because it started as 0 - as long as they don't interact with other things (outside the system) like friction against the table or somebody touching them.


That's like ours except the pipe and mass needn't have the same mass as each other.


Quote:

does a 1000 meter pipe length seem like a good round number.

Yea OK. I hoped to avoid too many numbers because they're so time consuming to work with. It doesn't really matter what the dimensions are. Either it always works or it never works.