From: fortunati.luigi@gmail.com   
      
   Sylvia Else sabato 12/11/2022 alle ore 12:08:50 ha scritto:   
   >> I am on board of trolley A and, during acceleration, I see trolley B   
   >> moving away from me by twice the initial distance (as Bell says in his   
   >> explanation).   
   >>   
   >> At the same time, I see the distances between the track sleepers (the   
   >> rail) shrinking.   
   >>   
   >> The effect of both causes increases the number of rails between me and   
   >> trolley B from 1 to 4, as is the case at the top of my animation.   
   >>   
   >> But 4 rails between me and B contrast with my speed over the ground   
   >> (v=0.866c range=2), for which there should only be 2 rails (twice as   
   >> much) between me and B (as is the case at the Bottom of my animation)   
   >> and not 4 rails.   
   >>   
   >> Hence my doubt that I was hoping someone could clarify, because if one   
   >> solution is right, the other is wrong (and vice versa).   
   >>   
   >> Luigi   
   >   
   > In this scenario, the choice you've made is that the two trolleys   
   > accelerate at the same rate as determined by the observer at rest   
   > relative to the initial state.   
   >   
   > They accelerate at different rates in their respective frames (which   
   > implies that differing, and indeed changing, forces are being applied to   
   > them). If the trolleys were connected by an inextensible tether, then it   
   > would break.   
   >   
   > Sylvia   
      
   So the scenario of the top of my animation   
   https://www.geogebra.org/m/ytws9kbr   
   where the ribbon breaks is correct.   
      
   But how do you justify the fact that reaching the speed v=0.866c   
   (gamma=2) the distance between A and B (in the reference of the trolley=   
      
   A) is 4 sleepers (quadruple) and not 2 (double)?   
      
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