A proton is two up quarks and a down quark, and a neutron is one up and two down. Their charges add to +1 and 0. The wavy lines are gluons, the carriers of the strong force, which bind the quarks and keep swapping a property called colour between them. Pairs of quarks and antiquarks (grey) flicker in and out of existence in between. The three quarks' own masses make up only about 1% of the proton's mass, and the rest is the energy of all this motion and binding.