Mass, Particles, and Quarks

Quark confinement demonstrates the equivalence of mass and energy discovered by Einstein. The mass of a particle made of quarks not only comes from the mass of the individual quarks, but also from their kinetic energy.

In a proton, only 1.3% of its mass comes from the mass of the three quarks. This is quite different from a nucleus which has less mass than its constituents.

Since the quarks in a proton or neutron have plenty of available kinetic energy, how are they bound? How come they cannot escape the proton? Since the strong force (unlike gravity) remains constant as a quark leaves a proton, more and more work must be done (work = force times distance). Thus, a quark can never get free.

This was a revolutionary idea.