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This question already has an answer here:

The mass of a proton is around 900 mega electron volts/c2. The mass of two up quarks and a down quark is about 10 mega electron volts/c2.

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marked as duplicate by John Rennie, David Hammen, Jon Custer, Community Jul 12 '17 at 0:00

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    $\begingroup$ Taken from Wikipedia: "... The extra energy of the quarks and gluons in a region within a proton, as compared to the rest energy of the quarks alone in the QCD vacuum, accounts for almost 99% of the mass ....." $\endgroup$ – jim Jul 10 '17 at 23:06
  • $\begingroup$ Possible duplicates: physics.stackexchange.com/q/207644/2451 and links therein. $\endgroup$ – Qmechanic Jul 11 '17 at 6:46
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Note that the quarks are bound by the strong interaction. The binding energy of the three-quark configuration in the proton is gigantic because the strong force is incredibly strong at short distances. This binding energy makes up the majority of the rest energy (mass) of the proton.

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  • $\begingroup$ It is not as simple as that. The three valence quarks can only be distinguished in a probabilistic manner , see profmattstrassler.com/articles-and-posts/largehadroncolliderfaq/… $\endgroup$ – anna v Jul 11 '17 at 4:42
  • $\begingroup$ @annav Right, but aren't the sea quarks and gluons included in any reasonable definition of the binding energy of the strong force? $\endgroup$ – probably_someone Jul 11 '17 at 4:44
  • $\begingroup$ well, it is not like the hydrogen atom, as he shows in the beginning of the article. The quarks are interchangeable. $\endgroup$ – anna v Jul 11 '17 at 4:46
  • $\begingroup$ @annav Yeah, but I don't think that conceptually alters my answer. It's still the strong interaction, which is made possible by the presence of the valence quarks, that's contributing most of the binding energy. $\endgroup$ – probably_someone Jul 11 '17 at 4:47
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The proton has three valence quarks, it is true, called current quarks, whose masses are very small. But it is in the quantum mechanical regime, a bound bag of these three valence quarks and its constituents are not just that , but also include an enormous number of quark antiquark pais and gluons playing ball with each other in the proton's volume:

proton

Read the link for details.

It is not only quantum mechanics that dominates this picture but also special relativity. In special relativity all those particles playing ball with each other have four vectors, which are additive. The total mass of the proton is the invariant mass of the sum of the four momenta of the constituents . The proton mass has been calculated in lattice QCD proving that the model of the nucleon used currently is valid.

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  • $\begingroup$ I am really curious why the downvote? $\endgroup$ – anna v Jul 11 '17 at 4:46
  • $\begingroup$ someone who dislikes gluons..? $\endgroup$ – Eliran Malka Nov 30 '18 at 19:09

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