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I Beginning through the Pedrotti optics book -- I have an energy question

  1. Feb 12, 2019 at 4:08 AM #1
    Hello. I started to work on pedrotti optics book (2nd edition) and i got confused about what is relativistic mass and why we use it rather than kinetic energy (1/2mc^2)?
    Also in the beginning of these explanations there is one equation i barely understand nothing out of it. Could you please explain this equation and where does it comes from please?
    P=sqr(E^2-(mc^2)^2/c . Thank you!
  2. jcsd
  3. Feb 12, 2019 at 7:56 AM #2

    Doc Al

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    Staff: Mentor

    As far as relativistic mass goes, it's rarely used these days. And that's not an expression for kinetic energy.
    That equation is the relativistic energy-momentum relationship. Start here: Energy–momentum relation
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