From: fortunati.luigi@gmail.com   
      
   Jonathan Thornburg [remove -color to reply] il 21/12/2023 09:19:38 ha=20   
   scritto:   
   > In my opinion a better analogy is to consider horizontal motion on the   
   > Earth's surface (which we can treat as being spherical for present   
   > purposes).   
   >   
   > Suppose you have two nearby ships on the Earth's (ocean) surface, whose   
   > courses are initially parallel (i.e., d/dt of the distance between them   
   > is zero), and that both ships move along "locally straight" lines, i.e.=   
   ,   
   > symmetrical hulls and rudders not deflected left or right.  Then each   
   > ship will travel along a great circle on the Earth's surface.  This   
   > implies that the ships paths will *converge* (i.e., d^2/dt^2 of the   
   > distance between them must be negative).   
      
   If there are 2 ships at the equator initially traveling south (and if=20   
   the rudder is always kept on starboard), they will end up meeting at=20   
   the south pole and if they initially travel north, they will end up=20   
   meeting in a completely different place (the pole north).   
      
     Instead, if there are 2 elevators whose cables break while they are=20   
   going up or down, they will always end up meeting in the same place:=20   
   the center of the Earth!   
      
   This happens because there is no force that changes the direction of=20   
   motion of the 2 ships but the force that reverses the direction of=20   
   travel of the 2 elevators that are going up when the cables break is=20   
   there!   
      
   Therefore, the comparison between the two conditions is not at all=20   
   correct, because in one case the forces are there and in the other they=20   
   are not.   
      
   Luigi Fortunati   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)