From: fortunati.luigi@gmail.com   
      
   Luigi Fortunati alle ore 05:02:06 di mercoledì 03/08/2022 ha scritto:   
   > [[Mod. note -- What does the word "simultaneously" mean?  In special   
   > relativity simultaneity is observer-dependent, i.e., different observers   
   > will in general not agree on whether two (spatially-separated) events   
   > are simultaneous.  There's no universal notion of "simultaneous".   
   >   
   > In the same way, whether or not the spring tilts is observer-dependent;   
   > there's no universal notion of tilt.   
      
   The tilt with respect to the floor of the wagon does not vary as the   
   observer changes!   
      
   [[Mod. note -- The whole point is that there's no generic   
   observer-independent "tilt with respect to the floor of the wagon".   
   Rather, different observers measure different tilts with respect to the   
   floor of the wagon.   
      
   If you disagree, please describe a way to (correctly) measure the tilt   
   which doesn't give different answers for different observers.   
   	[For example, suppose we mount a (level) protractor   
   	on the wagon and try to read the spring's tilt on the   
   	protractor scale.  We immediately run into the problem   
   	that the spring is falling, so we need to read the two   
   	sides of the protractor at the same time.... but different   
   	observers disagree about "the same time".]   
      
   The underlying logic of your apparent paradox (and the resolution that   
   "tilt" is observer-dependent) is very similar to that of the well-known   
   "stick and hole" apparent paradox, e.g., see sections 5 and 6 of   
     https://en.wikipedia.org/wiki/Ladder_paradox   
   or   
     http://www.relativitysimulation.com/Tutorials/TutorialMeterstickAndHole.html   
     https://physics.stackexchange.com/questions/83520/a-relativist   
   c-meter-stick-and-a-thin-disk   
     https://www.physicsforums.com/threads/meter-stick-slides-over-   
   -meter-wide-hole-at-a-high-speed.945765/   
   -- jt]]   
      
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