From: sylvia@not.at.this.address   
      
   On 29/07/2018 2:24 AM, Luigi Fortunati wrote:   
   > Sylvia Else ha scritto:   
   >> 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.   
   >   
   > Even when two heavy billiard balls collide, the contact occurs at a   
   > single point, but this does not mean that the force exchanged there must   
   > necessarily be negligible!   
   >   
      
   Forces do not get exchanged. Each billiard ball applies a force to the   
   other one. As with the other situation, you cannot expect to explain the   
   behaviour of the system by looking just at the point of contact.   
      
   Sylvia.   
      
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