71Since, Attraction can exist between two oppositely charged particles but In nucleus the Proton is positively charged while Neutrons are neutral. So Question arises How could they balance the force from the orbiting electrons.
So there was the need of other force. And the Idea of Nuclear Force evolved. This is analogous to Vander Waal's forces of gases. [However the former is very much stronger]
"The concept of a nuclear force was first quantitatively constructed in 1934, shortly after the discovery of the neutron revealed that atomic nuclei were made of protons and neutrons, held together by an attractive force. The nuclear force at that time was conceived to be transmitted by particles called mesons, which were predicted in theory before being discovered in 1947. In the 1970’s, further understanding revealed these mesons to be combinations of quarks and gluons, transmitted between nucleons that themselves were made of quarks and gluons. This new model allowed the strong forces that held nucleons together, to be felt in neighboring nucleons, as residual strong forces."