From: fortunati.luigi@gmail.com   
      
   Fixed one end of the spring to the ceiling and hanging a body at the   
   other end.   
      
   The point of contact (between the spring and the body) takes to   
   accelerate downwards, then decelerates, then stops and then returns to   
   accelerate upwards, thus initiating a continuous oscillating motion,   
   synonymous with variable acceleration that (according to the second   
   principle F=ma) requires the presence (at the point of contact) of a   
   continuously variable net force (increases, decreases, changes to,   
   returns to increase and so on without interruption).   
      
   Since the only two forces acting at that point are the gravity and the   
   tension of the spring, it is correct to state that the oscillation is   
   due to the variability of the resultant (at the point of contact)   
   between the force-weight action (on one side) and the reaction of the   
   spring tension (on the other)?   
      
   --   
   - Luigi Fortunati   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)