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Tell me why

  1. Jan 24, 2005 #1
    what is rest mass? why does a photon have rest mass zero? :uhh:
  2. jcsd
  3. Jan 24, 2005 #2
    Rest mass is the mass an object has when you are in its frame of refrence (IE its stationary to you). Photons have rest mass zero because they dont have any mass :)
  4. Jan 26, 2005 #3
    thank q for ur ans
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