From: pa@see.signature.invalid   
      
   Luigi Fortunati  wrote:   
   > Il 12/02/2026 07:30, Luigi Fortunati ha scritto:   
   > > The Wikipedia entry for "Elastic collision"   
   > > https://en.wikipedia.org/wiki/Elastic_collision   
   > > contains the following animation   
   > > https://youtu.be/wl0c6NMysY4   
   > > where the two bodies collide at point x and instantly reverse direction.   
   > [ ... ]   
      
   > I dispute what the moderator wrote.   
      
   > A body of mass 2m cannot bounce back (in place!) when it collides with a   
   > body of mass m,   
      
   And yet, it bounces back, though with a reduced velocity.   
      
      
   > otherwise a body of mass 3m, 10m, or 100m would also bounce back.   
      
   No, a body of mass 3m would stop cold, and bounce the body of mass m with   
   velocity 2*v.   
   More massive bodies would continue forward with reduced velocity, and bounce   
   the smaller   
   body with increased velocity.   
      
      
   > It's obvious that a body of mass 100m, colliding with a body of mass m,   
   > can only slow down but not stop in place and bounce back!   
      
   Slows down a bit and bounces the smaller body with velocity approaching 3*v.   
   The formulas are in the text above the animations. (Mind the signs of the   
   vA1,vB1 and vA2,vB2.)   
      
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   pa at panix dot com   
      
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