From: tjroberts137@sbcglobal.net   
      
   On 7/15/22 6:11 PM, Julio Di Egidio wrote:   
   > I think that more basic and to the point here was to note that   
   > centrifugal/centripetal are, as said, just two sides of the same one   
   > coin.   
      
   Not at all! They are VERY different: centripetal force is a real force,   
   usually one that keeps one object in orbit around another object;   
   "centrifugal force" is a fictitious "force" used in Newtonian mechanics   
   to permit one to act as if rotating coordinates were inertial, so one   
   can apply Newton's laws -- in general that is not sufficient and one   
   also needs "Coriolis and Euler forces" (which are also fictitious).   
      
   	[I put fictitious "forces" in scare quotes, because   
   	 they are not really forces.]   
      
   The difference is: a real force cannot be made to vanish by changing   
   coordinates, while a fictitious "force" will vanish in inertial   
   coordinates. As nature uses no coordinates, all natural phenomena must   
   be independent of coordinates; contrariwise, all coordinate-dependent   
   quantities are purely human inventions. Note this distinction is theory   
   dependent: in Newtonian mechanics the force of gravity is real, while in   
   General Relativity it is fictitious.   
      
   Ultimately all fictitious "forces" can be traced to geometry: in GR they   
   are directly related to specific components of the connection.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
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