I know that during certain nuclear reactions, the rest mass of the components is greater than the rest mass of the matter results because it lost potential energy. The implication is that the potential energy contributed towards that inertial (relativistic?) mass.
However the inertial mass $E$ for an individual particle is given by
$$E=\gamma m_0c^2 $$
there is no potential energy involved.
For a 2 particle system, the rest mass of the system would be to contribution from each of the rest masses, the contribution from the kinetic energies relative to COM, and the contribution from the potential energy. But I am not sure by what law we add this potential energy to the mass.
Is it that we are considering the average kinetic energy of the bound system and we are not actually considering the potential energy? Does the potential energy of hydrogen atoms come from the average kinetic energy of the constituent quarks and gluons, and in a helium these average kinetic energies are less?
