From: fortunati.luigi@gmail.com   
      
   In my animation   
   https://www.geogebra.org/m/sywszege   
   when the stone hits the wall, it experiences the blue force directed to   
   the left.   
      
   During the collision, the internal particles of the stone (in tension)   
   exert their force towards the right on the particle in front and   
   towards the left on the particle behind.   
      
   Is the resultant of all internal forces a zero force or is it a force   
   equal and opposite to the blue force exerted by the wall on the stone?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)