OK, you want maths?

Referring to my previous picture

p1 = momentum of plane
p2 = momentum of air pushed back by plane's propeller
p3 = momentum of pipe

total momentum of the whole system ptotal = p1 + p2 + p3

Initially everything's stationary and the plane's in the middle:
p1=0
p2=0
p3=0
ptotal=0+0+0 = 0

Then the plane starts flying:
p1=10
p2=-10
p3=0
ptotal=10-10+0 = 0

Then the air from the propeller hits the pipe
p1=10
p2=0
p3=-10 (notice that the pipe is moving!!!)
ptotal = 10+0-10 = 0

Then the plane hits the end of the pipe
p1=0
p2=0
p3=-10 + 10 = 0 (now the pipe stopped moving)
ptotal = 0+0+0 = 0


TOTAL MOMENTUM REMAINS ZERO AT ALL TIMES!!! You might be confused by the small movement of the pipe, and think that's propulsion, but turn down think street and work out why it's no use for a spaceship.



Edited by kallog (06/04/10 04:30 AM)