From: fortunati.luigi@gmail.com   
      
   Bruce Scott sabato 12/12/2020 alle ore 19:13:37 ha scritto:   
   >> The bridge and the train have the same length at rest.   
   >>   
   >> The bridge collapses only if the entire weight of the train rests on   
   >> it.   
   > [...]   
   >   
   >> [Moderator's note: This is essentially the same puzzle as the ladder   
   >> paradox, which even has its own Wikipedia entry.  In fact, it is closer   
   >> to the "man falling into grate" version originally discussed by the   
   >> late, great Wolfgang Rindler. -P.H.]   
   >   
   > The version we got in class (way back when) was the train entering the   
   > barn with the doors opening/closing just in time.  The answer, of   
   > course, is relativity of simultaneity.   
      
   But does the bridge collapse or does it not collapse?   
      
   [Moderator's note:  Answer per moderator's note here, as this has been   
   solved long ago.  The bridge collapses.  Forget the complication of the   
   bridge and the weight of the train causing it to break; just have a gap   
   where the bridge should be.  Does the train fall into the gap?  Yes.   
   See the "paradox" due to Rindler above.  Check this out:   
   https://www.youtube.com/watch?v=Xrqj88zQZJg  I think that some of the   
   confusion comes from first assuming that when the train is on the bridge   
   or the gap then it will fall, but in practice if the train were moving   
   that fast then it would just sail over the gap.  But if you assume that   
   it would fall when positioned over the gap, you also have to assume that   
   gravity is strong enough to pull it down.  -P.H.]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)