From: ram@zedat.fu-berlin.de   
      
   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.   
      
     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.   
      
     An acceleration can be identified with a force via F=ma.   
      
     I do not wish to discern between "real" and "apparent" forces,   
     but I'd like to say that in this case the motion of the   
     particle can be described in the cartesian coordinate system   
     more easily.   
      
     In the cartesian system, a uniform motion in two coordinates   
     also breaks down into two uniform motions in each coordinate.   
      
     In a polar coordinate system, a motion that is uniform when   
     both coordinates are considered in combination might not be   
     uniform anymore when only one coordinate is considered in   
     isolation.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)