From: gerry@bindweed.com   
      
   In article , fortunati.luigi@gmail.com   
   says...   
   >   
   > The spaceships A and B are at rest:   
   > A----------B   
   >   
   > Then B turns the engines on, and goes.   
   >   
   > In B's reference frame, the A spaceship is no longer at rest but goes   
   > away accelerating.   
   >   
   > Can we say that in the B reference frame there is a F force that   
   > accelerates A even though its engines are off?   
      
   No, because A is moving inertially.   
      
   If you want, though, you can say that there is a pseudo-force acting on   
   A, from the perspective of B's non-inertial reference frame.   
      
   A similar argument applies to concepts like centrifugal force.   
      
   - Gerry Quinn   
      
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    * Origin: you cannot sedate... all the things you hate (1:229/2)