1. The problem statement, all variables and given/known data I'm not sure how pions relate to the strong force. My notes say that only gluons propagate the strong force between quarks - holding a neutron together, and that residual force (I imagine between the quarks of neutrons and protons) holds neutrons and protons together in a nucleus. But the I also know that in scattering events between nucleons, virtual pions are present. But these don't change protons to neutrons as this is the weak force right? So what are pions doing?