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Rest mass

  1. Apr 2, 2014 #1
    Hi all. we know that the rest is the mass of an object within a coordinate system which has zero velocity, but how does it exist for an electron inside a crystal, which we call rest mass of electron, how electron exist with zero velocity.or we mean by zero velocity of electron with respect to an observer?
  2. jcsd
  3. Apr 2, 2014 #2


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    Try giving an electron a KE of a few eV. Now, try and calculate how much relativistic effects comes into play at such energies. Do you think it makes that much of a difference for a mass that we measure at such energies with the "rest mass"?

    Furthermore, inside a solid, the "effective mass" due to the many-body interactions has a greater effect on the "mass" of an electron (or quasi-electron) than the issue of relativistic mass in many cases.

  4. Apr 2, 2014 #3


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    When regarding mass, it's simpler and better to just regard the whole energy/mass of a bounded system together instead of trying to index them element by element. For example, the mass of a proton (~900MeV/c^2) is not equal to the mass of the three quarks (~2-5MeV/c^2) which compose it, but mostly due to the strong interaction between the quarks.

    Practically speaking this is what we do anyways when we put an object onto a scale for measurement.
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