From: fortunati.luigi@gmail.com   
      
   Jos Bergervoet alle ore 19:33:08 del 09/08/2017 ha scritto:   
   > Obviously it is important here to define 'acceleration' as the   
   > locally perceived (by T) acceleration. Incidentally, the other   
   > twin, T0, who is still on Earth, perceives an acceleration of   
   > 9.8m/s^2 all the time, whereas T, using the sling-shot return,   
   > perceives no acceleration at all during his journey.   
   >   
   > If you want to use another definition of 'acceleration' (or of   
   > 'transition' or of 'reference frame') the answers to your   
   > questions might well be different. These things are actually   
   > very difficult to discuss in words, without mathematical   
   > definitions.   
      
   Acceleration is variation of velocity in a given frame.   
      
   Is this definition of acceleration rigorous (and sufficient)?   
      
   --   
   Luigi Fortunati   
      
   Credere e' piu' facile che pensare   
   Believing is easier than thinking   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)