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You are correct. I was sloppy in my speaking. When two objects are bound together, their total energy is less than when they are separate. But that clearly implies that the mass of "free objects" is greater than their combined mass when they are joined together with that excess mass being converted to energy which is emitted during the formation. In the case of the quarks that make up the proton or neutron, their combined mass is considerably less than the their combined mass. What I was trying (not very well) to say, was where does this mass come from? We know that in "ordinary particles" that energy is given up by converting some of the mass of the constituents. But in the case of protons and neutrons, the energy that "creates" the mass that the protons and neutrons show us has to come from somewhere, and it seems that it must be the kinetic energy of the quarks and gluons that are "contained" within the composite particle.
Hugh wrote:
"The difference, originally quaintly called the "mass defect," is,
of course, the "binding energy" that serves to hold the nucleus together. ... So where does the "binding energy" that holds these particles together come from?"
I'm a bit confused here. I have thought that the binding energy
is the energy that a system *gives away* when bonds are formed;
the bonding could be chemical, nuclear or whatever. The mass of
the system decreases because part of the initial rest energy
('the mass defect') is transported to the surroundings or
manifests itself as kinetic energy of the products. Isn't this
the whole idea behind extracting nuclear power?
So I wouldn't like to talk about the binding energy as if it
were present in the system to keep it together. Should I correct
my view?