From: sylvia@not.at.this.address   
      
   On 28/07/2018 6:05 AM, Luigi Fortunati wrote:   
   > 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)?   
   >   
      
   The instantaneous net force at the point of contact has to be negligible   
   since the mass of a point is also negligible.   
      
   You cannot expect to explain the behaviour of the system by looking just   
   at a single point.   
      
   Sylvia.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)