From: helbig@asclothestro.multivax.de   
      
   In article ,   
   ram@zedat.fu-berlin.de (Stefan Ram) writes:   
      
   > Luigi Fortunati  writes:   
   >> And if even this answer is yes, is this force real or apparent?   
   >   
   >   Imagine a free particle is moving leftwards without forces   
   >   tangentially to a circle around a center:   
   >   
   >       C_____B_____A   
   >           .-'     '-.   
   >         .'           '.   
   >        /               \   
   >       ;                 ;   
   >       |        o        |   
   >       ;                 ;   
   >        \               /   
   >         '.           .'   
   >           '-._____.-'   
   >   
   >   Between A and B, the distance to the center is   
   >   approximatively constant. The velocity of escape from the   
   >   center is approximatively zero.   
      
   This is normally called the radial velocity; "escape velocity" has   
   another meaning.   
      
   >   Between B and C, the particle clearly moves away form the   
   >   center.   
   >   
   >   So the escape velocity (the change in the radial coordinate)   
   >   has increased.   
   >   
   >   The motion of the particle is not accelerated in cartesian   
   >   coordinates.   
   >   
   >   But when polar coordinates are used and then only the radius   
   >   coordinate is taken into consideration, there is an acceleration.   
      
   The DISTANCE has changed, but not the VELOCITY, so I see no acceleration   
   here.  (When an object is moving in a circle, the acceleration comes   
   from the fact that the straight-line motion is replaced by circular   
   motion, which corresponds to a pull towards the centre.)   
      
   --- SoupGate-Win32 v1.05   
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