XPost: sci.physics.relativity   
   From: uepe@gierrsw.pr   
      
   Tom Roberts wrote:   
      
   > 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   
      
   It's not even a formula, but rather a definition. You mix mass and   
   acceleration together in a bottle, what you get is a Force, since we want   
   to call it as such.   
      
   Could you please remind me your other question?   
      
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