From: tjroberts137@sbcglobal.net   
      
   On 9/4/19 1:12 AM, PengKuan Em wrote:   
   > Hello everyone, I search for an answer to a problem about length   
   > contraction.   
      
   It's rather a problem in your (mis)understanding of SR.   
      
   > If we have a ruler of length L, its near end is at x=0 and far end   
   > at x=L when stationary. If we put it in motion, its length is   
   > contracted to L/gamma.   
      
   ONLY when it is at rest in an inertial frame, and ONLY when observed   
   from some other inertial frame. Your scenario violates these conditions   
   for "length contraction" to hold.   
      
   When accelerating a ruler from rest, how the ruler behaves depends on   
   precisely how it is accelerated -- this OUGHT to be obvious. For   
   instance, you could push it from the back: the inertia of the front and   
   molecular dynamics imply the ruler will physically become shorter due to   
   inter-molecular strain. Or you could pull it from the front: it will   
   physically get longer due to inter-molecular strain. This is all   
   completely independent of SR. Note also that during the initial   
   acceleration the relative velocity is small so second-order effects such   
   as "length contraction" are negligible.   
      
   Your reference claims:   
   > Special Relativity cannot work with acceleration because of length   
   > contraction.   
      
   This is wrong. SR can handle acceleration just fine, but you must apply   
   the theory correctly: use the full Lorentz transform, not a comic-book   
   version of "length contraction". Your scenario has the added   
   complication that the ruler is not at rest in any inertial frame;   
   dealing with that requires careful analysis, and errors are easy to make.   
      
   Bottom line: when you make unphysical assumptions you can get unphysical   
   results.   
      
   Tom Roberts   
      
   --- SoupGate-Win32 v1.05   
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