From: tjroberts137@sbcglobal.net   
      
   On 11/18/17 3:40 AM, richard isakson wrote:   
   > Perhaps an historical perspective would help.   
      
   An ACCURATE perspective could be useful, but yours is just plain wrong.   
      
   > Why does the term "centrifugal force" even exist?   
      
   Because in the 19th century it was found useful.   
      
   > Before 1960-ish the basis of both statics and dynamics were the same: the   
   > vector sum of all forces must equal zero.   
      
   I have no idea why you say this; your "history" is wrong, and nothing   
   "changed" in the 1960s. Moreover, this statement is clearly wrong for   
   dynamics -- for the stone on a rope discussed in this thread, if the net   
   force on the stone were zero it would move in a uniform straight line;   
   it doesn't. (Implicitly using coordinates fixed to the ground.)   
      
   > [...] Later, dynamics was changed to say that the vector sum of all forces   
   > is equal to the accelerations times the mass.   
      
   This is very confused and historically just plain wrong. Dynamics was   
   not "changed", and F=ma has been used since the 17th century, not since   
   "1960-ish" as you claim.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)