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

Is there mass without momentum?

  1. Dec 4, 2011 #1
    There's something called "rest mass" that is the mass of a body in "rest". But since rest is relative it is impossible to surely know something's mass. We also know that mass increses with velocity, so it seems possible that mass is nothing but a "shaded" speed in a certain referential.
    Share your ideas about the subject.
  2. jcsd
  3. Dec 4, 2011 #2
    In my bathroom I am at rest relative to myself and the scale. I thought there was a different way of looking at it that didn't require relative mass per se, but an understanding of mass-energy, objects don't get harder to accelerate due to increased mass if you say F = (mass-energy) * acceleration, then it is due to increased energy?
  4. Dec 4, 2011 #3


    User Avatar

    Staff: Mentor

    The name "rest mass" is a historical artifact and can be rather misleading. Physicists nowadays prefer to use the name "invariant mass." It can always be calculated from an object's momentum and energy using

    [tex]E^2 = (m_0 c^2)^2 + (pc)^2[/tex]


    [tex]m_0 c^2 = \sqrt{E^2 - (pc)^2}[/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook