XPost: sci.physics, sci.space.tech   
   From: mooregr@greenms.com   
      
   "John Schoenfeld"  wrote in message   
   news:a98beaaa.0307140646.5c89382d@posting.google.com...   
   >   
   > Certainly not. You could add holes along the side of the rocket so   
   > that the air-pressure can let the explosion exit without affecting the   
   > overall net upwards momentum. Although this would be inefficient, it   
   > demonstrates that the CAUSE of upwards acceleration is IRRESPECTIVE of   
   > the exit direction of expelled mass.   
   >   
      
   No you can't since the "explosion" exiting would now push against the rocket   
   from all sides and the rocket would not move.   
   >   
   > No it is not. Imagine a stationary black-box floating in space. One   
   > wall of the box is hard iron and the opposite side is ellastic. If a   
   > ball is thrown from the middle at the hard iron wall there will be a   
   > high-impulse transfer of momentum from the ball to the box.   
      
   First, you've already ignored, "what throws the ball."  Hint, if it's   
   attached to the box (saw a cannon) the box will move backwards until the   
   ball hits the front wall.  At that point the box will move forward and end   
   up where it started.  No net movement.   
      
   If the cannon is not attached, it will be propelled backwards, hitting the   
   back wall, forcing the box backwards.  The ball hitting the front will then   
   push the box forwards the same amount.  No net movement.   
      
   >Relative   
   > from the center of the box (which at this point is moving), the ball   
   > now approaches the opposite ellastic wall in which it inevitably   
   > collides with and transfers the same momentum but in the opposite   
   > direction bringing the box to rest again. However, the elastic wall   
   > collision was low-impulse and took longer for the momentum to be   
   > conservered. Irrespective of momentum conservation, there is an   
   > overall displacement.   
   >   
      
   No, there isn't.  The box returns to its original position.   
      
   > At this point we have the box at rest yet it is displaced from its   
   > original position, however in future time this same effect will occur   
   > but in the opposite direction and thus the overal motion of this   
   > contraption would be to OSCILLATE about the original position. So   
   > technically speaking, its not inertial propulsion yet as the center of   
   > mass is constant.   
   >   
      
   THat part is right.  All it will do is oscillate.   
      
   > So the third and final requirement would to have a constant stream of   
   > balls colliding just as the first one thus always staying one step   
   > ahead of the "backwards oscillation phase".   
   >   
      
   Again, this simple doesn't work.   
      
      
   >   
   >   
   >   
   > >   
   > > > All that needs to be done is to make the upwards push a greater   
   > > > impulse than the downwards push - the rocket would essential jerk its   
   > > > way upwards - after all there is no "conservation of displacement"   
   > > > with such an inertial system.   
   > >   
   > > There is conservation of momentum, and you just proposed to violate it.   
   > > This is a stiction (static friction) drive, and works only when in   
   > > contact with some other body.  The movement comes from the difference   
   > > between static and sliding friction.  And, BTW, if you want a drive that   
   > > only works when in contact wiith a larger body, there are much better   
   > > ones (the wheel comes to mind).   
   > >   
   > > Such a drive is utterly useless in space, however.  Jerk your rocket   
   > > around all you want, it'll never make any net progress at all.   
   >   
   > Sure you can, read above.   
      
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