From: dr.j.thornburg@gmail-pink.com   
      
   In article , I wrote:   
   [[analysis of Luigi's system]]   
      
   Two small corrections to my derivation of the water pressure inside B   
   as a function of r (the distance from the rotation axis):   
      
   Correction #1: I wrote:   
      
   > The net force acting   
   > on the volume element of water due to the pressure gradient is then   
   > the difference between the forces acting on the two opposite flat faces   
   > of the volume element, i.e.,   
   >   
   >   dF_net = p(r+dr) dA - p(r) dA                                    (6)   
   >   
      
   Here (right after equation (6)) I should have inserted the phrase   
      
     where p = p(r) is the pressure as a function of position.   
      
   Correction #2: A few lines later, I wrote:   
      
   > Also, by Newton's 2nd law (since this volume element of mass dm is moving   
   > with centripetal acceleration $a$), there must be a net force acting on   
   > the volume element of   
   >   
   >   dF_net = dm a                                                    (7)   
   >          = dA dr a    [here we're using (5)]                       (8)   
      
   Oops, I left out a factor of   rho   in the right hand side of (8),   
   i.e., I should have written   
      
       dF_net = dm a                                                    (7)   
              = dA dr rho a    [here we're using (5)]                   (8)   
      
   It may also be worth noting that nothing in my analysis made use of the   
   fact that A and B are actually in *circular* motion about their rotation   
   axis; I only used the fact that they have a net acceleration (which I   
   called $a$) in the direction towards that axis, i.e., to the left in my   
   free-body diagrams.  So, my analysis, including those free-body   
   diagrams, would have been unchanged had the physical situation instead   
   been that the string had a rocket with thrust $T$ attached to it,   
   accelerating A and B to the left with respect to an inertial reference   
   frame.   
      
   --   
   -- "Jonathan Thornburg [remove -color to reply]"    
      on the west coast of Canada   
      "quit   When the quit statement is read, the  bc  processor is terminated,   
              regardless of where the quit statement is found.  For example,   
              'if  (0  ==  1)  quit' will cause bc to terminate.   
                                                    -- old Unix manpage for 'bc'"   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)