From: henry@spsystems.net   
      
   In article <1103238805.284083.53000@z14g2000cwz.googlegroups.com>,   
   queetzal  wrote:   
   >Imagine that the ball receives a short upwards tap,or impulse, once per   
   >rev, as it crosses the 3 o'clock(East) position. My contention is that   
   >the orbit will be tilted up a little bit on each tap and the tilt will   
   >be such that the whole orbit essentially rotates about the north-south   
   >axis. In other words the high point of the orbit is at the point where   
   >the taps occur. There is no "gyroscopic precession" acting to cause a   
   >phase delay such that the high point of the new orbit is reached at the   
   >12 o'clock position.   
      
   I'm afraid you are incorrect.  The ball *does* have angular momentum, and   
   precession is indeed involved.   
      
   When you give it a tap at the 3 o'clock position, that doesn't instantly   
   move it upward.  You've changed its velocity, not its position.  The tap   
   sets it *moving* upward as it heads northward.  It continues to move up so   
   long as it's moving north, i.e. until it reaches the 12 o'clock position.   
   So the high point is indeed at 12 o'clock.   
      
   >My ball on a string example is supposed to show that precession   
   >disappears when talking about a point mass and a point force and only   
   >reappears when the force is spread over a 90 degree area.   
      
   It's a general property of rotating mass -- and yes, even a point mass   
   going around in a circle qualifies -- and does not require either   
   distributed mass or distributed force.   
      
   I do orbital mechanics professionally, by the way (when funding permits).   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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