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Potential energy contributes to the mass

  1. Apr 18, 2006 #1
    i read in many places:even if you put together identical bricks it turns out that the mass of the object you construct depends on how ou put the bricks together.
    do they mean that the potential energy contributes to the mass of the constructed object?
     
  2. jcsd
  3. Apr 18, 2006 #2

    Meir Achuz

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    Give a reference to one of the many places.
     
  4. Apr 18, 2006 #3
    give google to look for
    Physics 209 last revised 3-2-01
     
  5. Apr 18, 2006 #4
    i find the same thing in
    n.david.mermin it's about time princeton university press 2005
     
  6. Apr 18, 2006 #5

    jtbell

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    OK, I found it. It's obviously using "bricks" as a metaphor for constituents of a composite object.

    In what follows, by "mass" I mean what is often called "invariant mass" or "rest mass", as does that article.

    Yes, the mass of a composite object or system does not necessarily equal the sum of the masses of its individual components. The potential energy of the system contributes to the mass of the system. Atomic nuclei are a well-known example: the mass of a nucleus is smaller than the sum of the masses of the individual protons and neutrons. If the individual components have kinetic energy in the reference frame in which the system as a whole is at rest (total momentum = 0), that contributes to the mass of the system as well.
     
  7. Apr 18, 2006 #6

    Meir Achuz

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    Physics 209 last revised 3-2-01 is too long for me to read.
    I don't always agree with Mermin, especially on EPR, but I'll buy
    Bell's answer.
     
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