In my A-Level physics notes on Nuclear Physics, my teacher states the following two points (taken directly from his notes):
In an unbound system (e.g. 6 individual protons and 6 individual neutrons), the rest mass of the composite system is greater than the sum of the rest masses of the separated particles by an amount equal to the kinetic energy of the amalgamating particles at combination.
In a bound system (e.g. a [here he had the symbol for a C-12 atom] nucleus), the rest mass of the composite system is less than the sum of the rest masses of the separated particles by an amount called the binding energy ∆E.
I understand the concept of the changing mass of the particles related to their potential energy, but my question is about certain words that he used in these statements:
What does ‘unbound composite system’ mean? It seems somewhat of a contradiction.
I’m not entirely sure about the energy difference being described in the first point (is this a theoretical kinetic energy or are the particles actually moving?)
In the second point he appears to compare the combined particles (a nucleus) to the seperated particles, all under the banner ‘bound system’. I don’t understand that.
Many thanks, Hugo