I think you understood the first time.
Originally Posted By: paul

and lets put all the compressed air inside a air tank at one end of the ship.

and its still inside the 60 inch diameter pipe and the pipe is still 500 ft long.


the tank is inside the 500 ft pipe.

there is space between the tank and the pipe.

so that the air inside the pipe presses against the entire inside area of the pipe.

Originally Posted By: ImagingGeek
Regardless, the math is the same.



what math are you refering to.
the
Originally Posted By: ImagingGeek
since p(air) = 100kg*m/s; p(bulkhead) also = 100kg*m/s


If you begin with 100 psi tank pressure
and
14.7 psi external pressure in the pipe.

you dont get an immediate equalization between the two.

you would end up with apx 10 psi inside the pipe after the
pressures have equalized.

its a 1000 cu ft tank inside a apx 10,000 cu ft area so the air
in the tank expands inside the pipe and the pressure reduces as it expands.

the force that you are referring to is fantasy , the same force is applied to both ends and to every square inch of the inside of the pipe.

thereby , no net force from the air acting against the pipe.

and I might add that the force caused by the (air pressure) is multiplied by the entire inside area of the pipe.

not just the end that you choose.

ie..
Originally Posted By: ImagingGeek
p(bulkhead) also = 100kg*m/s


but go ahead and calculate the force that you think is applied to the end of the pipe , it will be the same force that is applied to the opposite end.

thus no net effect.

I agree the pipe will not move for long , it will only move as long as the air has a differential pressure that will cause a net force in the opposite direction of air flow.

exactly like a jet plane would move if it were inside a larger pipe.

and if the jet plane was in the larger pipe in space and it pressed against the end of the pipe , it would transfer its momentum to the pipe , and if it kept on thrusting forward the pipe would continue to move forward.

but I suppose you have a answer to that also...

and it is a no-thinker

zero net force , right?

and in this scenario the air thrust comming out of the tank is exactly the same as thrust comming out of a jet aircraft.










_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.