From: tjroberts137@sbcglobal.net   
      
   On 12/19/17 12/19/17   2:11 PM, Luigi Fortunati wrote:   
   > Tom Roberts lunedì 18/12/2017 alle ore 22:11:45 ha scritto:   
   >> ...   
   >> "Centrifugal force" is purely an artifact of using rotating coordinates   
   >> (implicitly those of your car's interior), and is a fiction invented to   
   >> permit one to apply Newtonian mechanics in a rotating frame.   
   >   
   > Also the centrifugal force that pushes me outwards (tied to the seat   
   > belts), is an "artifact"?   
      
   You are confused.   
      
   In your car, belted in, as the car turns left, the seat belts pull you   
   to the left [@] -- to the INSIDE of the turn. There _IS_ no force   
   outward, it's just that your body wants to move inertially (i.e. in a   
   straight line), and with the car turning left, the car and seat belts   
   must exert a leftward (inward) force on your body to keep you in your   
   seat.   
      
       [@] Belts are flexible and cannot push significantly.   
      
   Put a frictionless horizontal table in the car, and place a small   
   frictionless object on it, initially at rest relative to the table with   
   the car moving uniformly in a straight line relative to the ground. Now   
   let the car turn left. Seen from coordinates fixed to the ground, the   
   object simply moves in a uniform straight line. Seen from coordinates   
   fixed to the car interior, the object accelerates to the right -- to   
   permit one to apply Newton's laws in these coordinates one must INVENT a   
   "centrifugal force" that is directed outward [#]. The fact that the   
   object moves in a uniform straight line relative to the inertial   
   coordinates of the ground shows there is no actual force on the   
   object. The "centrifugal force" invented for the (rotating) car   
   coordinates is FICTITIOUS, an artifact of the non-inertial coordinates.   
      
       [#] And also a Coriolis force....   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)