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Do different reference frames agree with total energy?

  1. Jan 9, 2013 #1
    I know total energy is conserved, but does this mean that different frames agree on the total energy of a particle?

    I'm assuming they don't agree on energy, because if I measured the total energy of a particle moving relative to me (which would equal the rest energy plus its kinetic energy) surely this can't be the same as the total energy of the particle measured by someone in a frame where the particle's at rest (where the total energy would just be its rest energy). Or am I going wrong somewhere?

    Thanks :)
  2. jcsd
  3. Jan 9, 2013 #2


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    Science Advisor

    Indeed not: if you measure the energy of a massive particle at rest relative to you and then boost to the frame of an observer who has a non - vanishing relative velocity in say the +x direction then under a lorentz transformation the energy is mapped as [itex]m_{0}c^{2} \rightarrow \gamma m_{0}c^{2}[/itex].
  4. Jan 9, 2013 #3


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    Staff: Mentor

    No. This is true both in relativistic and non-relativistic physics, by the way. Energy is conserved in any inertial reference frame, but is it not invariant between inertial reference frames.
  5. Jan 9, 2013 #4
    Thanks guys :D
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