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E=mc^2 and is it possible E/c^2=m

  1. Feb 27, 2009 #1
    can anyone explain in simple terms Einstein's equation E=mc^2 and is it possible E/c^2=m, because it is said mass can neither be created nor destroyed!
    Last edited by a moderator: Feb 27, 2009
  2. jcsd
  3. Feb 27, 2009 #2


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  4. Feb 27, 2009 #3


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    Re: E=mc^2

    That last statement is not true in relativity. It is total mass and energy that is conserved.
  5. Feb 27, 2009 #4
    Re: E=mc^2

    Every time people get confused by the difference between rest(invariant) and relativistic(conserved) mass.

    When people come here after reading E=mc^2 they are definitely talking about the relativistic mass!
  6. Feb 27, 2009 #5
    Re: E=mc^2

    Also,wikipedia has a long winded explanation at

    In brief, Einstein's equation relates the amount of equivalent energy in a rest mass.
    A small amount of mass,m, produces a lot of energy, E, because the constant c is really,really big. for example,
    E (in joules) = m (in kilograms) multiplied by (299,792,458 m/s)^2.

    So for example, less than 1% of two pounds of uranium produced the atomic bomb blast (energy) at Hiroshima. (The other 99% was waste radioactive material.) And when the fission is controlled as in a nuclear power plant by slowing the cascading neutrons, a lot of power (energy) can be extracted over a longer period of time to produce useful electricity and steam (two forms of energy).(And there is still a lot of radioactive waste.)
  7. Feb 27, 2009 #6
    Re: E=mc^2

    The same is applicable to the relativistic mass:

  8. Feb 27, 2009 #7
    Re: E=mc^2

    Post #6 is entirely correct...
    I was keeping it SIMPLE.....
    The energy E can be considered as ALL forms of energy, heat, liner and angular momentum, kinetic and potential, gravitational, etc, as well as the component from rest mass....

    If the mc2 equation is written as moc2 then one knows its rest mass for sure....but someone asking the question posted here is unlikely to make that distinction....
  9. Feb 28, 2009 #8
    Re: E=mc^2

    Yes, but how would your reply the question beginners ask many times:

    E=mc^2, so energy can be convertedinto mass and vice versa?
    Answer depends on what notion of mass do you use.
  10. Feb 28, 2009 #9
    Re: E=mc^2

    what do you mean when you say "notion of mass"??
  11. Feb 28, 2009 #10
    Re: E=mc^2

    I mean, answer is different for the rest and relatiistic mass.
  12. Feb 28, 2009 #11


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    Re: E=mc^2

    The question itself is incorrect. It should be "Can matter be converted into energy".
  13. Feb 28, 2009 #12
    Re: E=mc^2

    How different is the answer for fission and fusion??? anybody know?? Seems like it should be small....energy released is related basically to binding energy of the nucleus, right???

    With high energy particles, as in acclerators, I can see momentum could be significant...relativistic considerations become significant....
    Last edited: Feb 28, 2009
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