From: nedlatham@woden.valhalla.oz   
      
   Tom Roberts wrote:   
   > Luigi Fortunati wrote:   
   > >   
   > > The sacrosanct formula F=ma says that if we exert a force F on   
   > > the mass , the mass accelerates.   
      
   It's an equation, Luigi, ma is the fromula.   
      
   > No formula is "sacrosanct", because EVERY equation of physics is   
   > valid ONLY when the conditions for its derivation are met.   
   > This formula, like so many others, is valid ONLY when values are   
   > measured relative to a locally inertial frame.   
      
   Crap. It doesn't matter *what* frame is used. The only requirement   
   is that *one* frame be used.   
      
   > IOW: before applying a formula you must know that each symbol   
   > in it means, and must be sure to apply and conform to those   
   > meanings.   
      
   Congratulations, Roberts. You got something right.   
      
   > When B turns its engines on and then uses coordinates in which   
   > B is at rest, there is no expectation whatsoever that the above   
   > formula applies, because those coordinates are not a locally   
   > inertial frame.   
      
   Irrelevant. One frame only is being used. The equation applies.   
      
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