From: tjroberts137@sbcglobal.net   
      
   On 11/8/17 11/8/17   2:03 AM, Luigi Fortunati wrote:   
   > The sacrosanct formula F=ma says that if we exert a force F on the mass ,   
   > the mass accelerates.   
      
   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.   
   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.   
      
   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.   
      
   Tom Roberts   
      
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