Question

what are the similarities between nn and pp forces

Answer 1

The nuclear force between two nucleons is charge independent. By this we mean that the strong interaction between two protons or two neutrons or a neutron and a proton is the same. (Of course, there will be differing electromagnetic forces in these cases). Evidence for the charge independence of nuclear forces can be found in nucleon-nucleon scattering and in the binding energies of light mirror nuclei.