XPost: sci.physics, sci.space.tech   
   From: bondage@frontiernet.net   
      
   John Schoenfeld wrote:   
      
   [snip]   
      
   > > Um, yes, it is.   
   >   
   > 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. 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.   
   >   
   > 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.   
   >   
   > 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".   
      
      I think some past claims of reactionless drives that allegedly   
   reduced their weight (though never to zero, it seems) on scales, had   
   more to do with a similar phenomenon in the springs of the scale, then   
   actually providing a net upward force. Time your oscillations right, and   
   you can fool the scale, but not Mother Nature....   
      
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