humm, I've been wondering: the mass of a nucleus is less than the sum of the masses of the constituent nucleons because of the binding energy. This is how we can get energy out of fusion and fission events. on the other hand, the mass of a proton or a neutron is MORE than the sum of the masses of the constituent quarks. Afaik, both the binding of a nucleus and the binding of a proton are consequences of the strong force, so how come one type of binding increases the mass while the other type decreases it? Thanks.