Subject: Aren't mass-energy and potential energy redundant?

When nuclear rearrangements occur, the rest mass of the nuclei change. The 
change in binding energy is then calculated by using the change in rest mass 
and Einstein's mass-energy relation (E=mc2). But, it seems that the energy 
release during the formation, say, of a helium nucleus can be explained by 
the nuclear potential energy released by the protons and neutrons as they are 
brought close together. The nuclear force does positive work, making the 
change in potential energy negative (meaning the particles are releasing 
potential energy) - just as a falling object in a gravitational field turns 
gravitational potential energy into kinetic energy. So why is there a change 
in rest mass of the nucleons as well? This seems like a redundant reason for 
the release of energy in this nuclear process. How does this seemingly double 
explanation for the energy release jive with the law of conservation of energy? 
Of course, I understand that the same type of mass loss occurs in chemical 
reactions, apparently making the concept of chemical potential energy redundant 
as well?

Thank you for your consideration of this question!

Patrick Harmon
AP Physics Teacher
Country Day School, Costa Rica

Re: Aren't mass-energy and potential energy redundant?