From: fortunati.luigi@gmail.com   
      
   While walking in the mountains, a man falls into a crevasse and, as he   
   goes down in free fall, he sees the mountain accelerate upwards.   
      
   Instead, those who are on the mountain see the man accelerating   
   downwards.   
      
   But who is really accelerating? Are the two accelerations both real or   
   only one is real while the other is only apparent?   
      
   To find out, we just need to understand towards which point man and the   
   mountain (with the entire Earth) are moving.   
      
   Obviously, man and the Earth both head towards the common center of mass   
   which (for all practical purposes) coincides with the center of the   
   Earth.   
      
   And if the center of the Earth is already at the common center of mass,   
   it doesn't need to move to reach it.   
      
   So the Earth does not accelerate, it is not an accelerated reference   
   system.   
      
   Instead, man (who is far from the common center of mass) must accelerate   
   in order to reach it and, therefore, it is an accelerated reference   
   system.   
      
   Between the man in free fall and the mountain, it is certainly not the   
   mountain that accelerates!   
      
   Luigi Fortunati   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)