Why is there an attractive force between two protons inside the nucleus?
Nucleons (protons and neutrons) both have a strong nuclear force with each other. The protons being charged have an additional force with other charged particles, including other protons. The nuclear force is short range while the electrical force can act up to longer distance. We cannot have a nucleus with only two protons, because the electrostatic force would pull such a nucleus apart. However if in addition to two protons you put in a neutron we do get stability because neutron, being neutron, has only a nuclear force, which helps to cancel the repulsion of the two protons. This nucleus is called Helium 3.
