XPost: sci.physics   
   From: relativity@paulba.no   
      
   Den 01.01.2026 17:19, skrev Stefan Ram:   
   > "Paul.B.Andersen"  wrote or quoted:   
   > :that mass could be converted to energy as   
   > :predicted by Einstein's E = mc².   
      
   I resent very much that you:   
   1. Break threads so it is impossible to see to what you are responding.   
   2. Paraphrase and not quote.   
      
   I can guess that you were responding to my statement:   
     "The atom bomb proved in a very convincing way   
      that mass could be converted to energy as   
      predicted by Einstein's E = mc²."   
      
   This statement isn't very precise, but not wrong.   
   So let's look at a more precise statement about   
   what is happening in an atomic fission bomb:   
      
   One possible fission process is:   
      
   1n + U-235 → Ba-141 + Kr-92 + 3n   
      
   The atomic weight (mass) of these are:   
      
   Left side:   
   1n      1.008664  u   
   U-235 235.0439299 u   
   -------------------   
          236.0525939 u = 3.919748214E-25 kg   
      
   Right side:   
   Ba-141   140.914412 u   
   Kr-92     91.926156 u   
   3n         3.025992 u   
   ---------------------   
             235.866560 u = 3.916659047E-25 kg   
      
   Lost mass: m = 0.1860339 u = 3.089167695E-28 kg   
      
   E = mc² ≈ 2.776404839E-11 J   
      
   >   
   >    I can spot three mistakes here right off the bat.   
   >   
   >         First, the phrase "mass could be converted to energy" is based on   
   >    a misconception, since mass already /is/ a form of energy - there's no   
   >    "conversion" happening. It's like saying, "water can be turned into a   
   >    liquid" - no, water /is/ a liquid.   
      
   Note that m = 3.089167695E-28 kg is the _lost_ mass,   
   it doesn't exist any more.   
   So where has it gone?   
   It is converted to E = mc² ≈ 2.776404839E-11 J of _kinetic energy_.   
   Kinetic energy is not mass. Thus "convert".   
      
   >   
   >         Second, "E=mc^2" only applies to systems at rest. In general,   
   >    it's "E^2=(mc^2)^2+(pc)^2", where "p" is the system's momentum.   
   >    (That basically says mass is the magnitude of the four-momentum.)   
      
   E = mc² is the energy content, or the energy equivalent of   
   the mass m. Mass is invariant, so this equation is valid for   
   all speeds of the mass.   
      
   However, the _total_ energy of a moving mass is:   
   E = mγc² = mc² + (γ-1)mc²   
   The first term mc² is the invariant energy content of the mass m,   
   the second term is the kinetic energy of the mass m.   
   Kinetic energy is not mass!   
      
   >   
   >         Third, mass is conserved in nuclear fission. This point is often   
   >    explained incorrectly, even in otherwise solid textbooks like Grif-   
   >    fiths.   
      
   Could it be that you are wrong and the textbook is right? :-D   
      
   Before the fission the mass of the U-235 nucleus + 1 neutron   
   is: m₁ = 3.919748214E-25 kg   
      
   After the fission the mass of the Ba-141 and Kr-92 nuclei + 3 neutrons   
   is: m₂ = 3.916659047E-25 kg.   
      
   So the mass isn't conserved, m = m₁-m₂= 3.089167695E-28 kg has   
   disappeared because it is converted to kinetic energy which is not mass.   
      
   The energy is conserved, though.   
      
   Energy before fission:   
   Energy content of mass m₁ = m₁c² = 3.522894007E-8 J   
   Total energy before fission E₁ = 3.522894007E-8 J   
      
   Energy after fission:   
   Energy content of mass m₂     E  = m₂c²      = 3.520117602E-8 J   
   Kinetic energy from lost mass K  = (m₁-m₂)c² = 2.776404839E-11 J   
   Total energy after fission    E₂ = E + K     = 3.522894007E-8   
      
   E₁ = E₂ energy conserved   
      
      
   --   
   Paul   
      
   https://paulba.no/   
      
   --- SoupGate-DOS v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)