XPost: sci.physics   
   From: PointedEars@web.de   
      
   Paul.B.Andersen wrote:   
   > 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".   
      
   /Non sequitur./   
      
   >>         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.   
      
   The first wording is simply wrong.  E (better: E₀) is the *rest* energy of   
   _an object_ whose mass is m.  One can also call that the energy content _of   
   that object_ at relative rest (as Einstein did, but this wording is   
   obsolete), but NOT "of the mass".  Mass is a quantity, not a object; a   
   quantity has no content.   
      
   > Mass is invariant, so this equation is valid for all speeds of the mass.   
      
   Again, mass is a quantity, NOT an object.  It does not make sense to say   
   "speeds of the mass".  That makes as much sense as e.g. "mass of the charge".   
      
   > 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,   
      
   No, the first term is the rest energy equivalent to the mass m.   
      
   Mass does not have an energy content, _objects_ have.   
      
   > the second term is the kinetic energy of the mass m.   
      
   No, it is the kinetic energy of an _object_ with mass m and relative speed   
   v, hidden in γ = γ(v).   
      
   > Kinetic energy is not mass!   
      
   And mass is NOT energy or "has energy".  You would be well to realize that.   
      
   >>         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   
      
   He is wrong, obviously.  But you are also wrong in multiple respects:   
      
   > 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,   
      
   Correct.   
      
   > m = m₁-m₂= 3.089167695E-28 kg has disappeared because it is converted to   
   > kinetic energy which is not mass.   
      
   Again: NOT the mass is partially converted to kinetic energy, but the rest   
   energy E_0 = m c^2 *equivalent to* the mass m.   
      
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   PointedEars   
      
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