If the pipe travels its length, then obviously none the air in it can remain where it was.

I never said that the air would stay where it was.

the majority of the air moves from the air tank to the pipe.

So any air that was going in the opposite direction to the pipe has to change direction. That imparts a force to the pipe pushing it backwards.

I agree that the air will be changing direction inside the pipe as the air settles inside the pipe.

but the forces that the air will impart to the pipe during the settling process will not all be in the direction
that would slow the pipe.

the air will apply the same force to the front of the pipe as it will the end of the pipe but most of this force will be to the sides of the pipe.

in other words the negative forces and the positive forces that the air leaving the nozzle applies to the pipe will cancel each other out.

leaving the force generated by the nozzle as the dominate force.

I think there is an easy way to settle this using a experiment.

using pvc pipe and a couple of valves compressed air and water.

and a swimming pool in place of outer space.

releasing the water that is being compressed by air through a pipe that connects to another much larger pipe , should
provide enought visual evidence.

Edited by paul (03/10/11 11:53 PM)
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.