Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Einstein's potential energy equation

  1. Oct 11, 2003 #1
    What happened to the 1/2 in the transformation of classical potential energy equation to Einstein's potential energy equation. Is it dropped because giving off all rest energy would require annhilation of a particle pair thereof 1/2mv2+1/2mv2=1mv2 gets rid of the half?
    Last edited by a moderator: Feb 6, 2013
  2. jcsd
  3. Oct 11, 2003 #2


    User Avatar
    Science Advisor

    Re: question

    What do you mean by "Einstein's potential energy equation"? I don't understand the question. Do you mean to compare mc^2 with (1/2)mv^2? Apples and oranges?
  4. Oct 11, 2003 #3
    Potential energy doesn't equal 1/2mv^2(that's kinetic energy) it equals mgh

    I think you are asking about the energy E = mc^2 equation relating to classical systems.

    First E = mc^2 is only for stationary objects. The actual equation is E = mc^2/[1-((v^2)/(c^2))]^1/2(you see now why when discussing it in general people assume v = 0)

    Einstein's equation deals with the total energy of an object at any speed. and the derivation can be found in most Modern Physics books( a convineince for me because I don't remember it off the top of my head)
  5. Oct 11, 2003 #4


    User Avatar
    Science Advisor

    kinetic energy from Einstein

    where m is rest mass.
    Expand Lorentz term in power series:
    Net result:
    The first 2 terms are the energy due to rest mass and the kinetic energy.
  6. Oct 16, 2003 #5
    whats so difficult about my question krab all i was asking was how come there is no half in the rest energy equation.
  7. Oct 16, 2003 #6


    User Avatar
    Science Advisor

    Well, then it's been competently answered by Mathman and VBPhysics.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook