From: nospam@de-ster.demon.nl   
      
   Luigi Fortunati  wrote:   
      
   > Circular motion without centripetal force is impossible.   
   >   
   > And then we must find a plausible explanation for this case.   
   >   
   > There is a rotating table and a disc without friction.   
   >   
   > If a person in the laboratory gently lays the disk on the rotating=20   
   > table and if the friction is (really) 100% absent, the disk, in the=20   
   > absence of friction, can not be dragged from the table, so it remains=20   
   > still while the table turns downstairs without disturbing.   
   >   
   > For the observer who rotates with the table, the disk travels around a=20   
   > circle without ever moving away or nearing the center of rotation.   
   >   
   > How can we justify the rotary motion in the accelerated reference if no=20   
   > centripetal force acts on the disc?   
      
   You forgot about the Coriolis force.   
   Do the sums, and you find that the Coriolis force on your disc   
   balances the centrifugal force, and that at any radius.   
      
   Slight generalisation: Satellite motion in a co-rotating frame.   
   For geostationary orbits the gravitational force   
   balances centrifugal force, and the sat is at rest.   
   (so no Corilolis force)   
   For any other altitude of a circular orbit you can find   
   the orbital speed fromm the needed Coriolis force.   
      
   Jan   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)