Strong Nuclear Force

The strong nuclear force is what binds protons and neutrons together inside a nucleus. Some attractive force has to be doing this, because otherwise the electric repulsion between the positively charged protons packed closely together would blow the nucleus apart instantly — and that attractive force cannot be gravity, which is far too weak at nuclear scales. The strong nuclear force is the answer: it is the strongest of all four fundamental forces, roughly a hundred times stronger than the electromagnetic force, and it is charge-independent — it acts with equal strength between two protons, between two neutrons, and between a proton and a neutron alike. Its reach, however, is tiny — of order nuclear dimensions, about $10^{-15}$ m — which is why it is felt only inside the nucleus and not beyond it. Notably, the electron does not exp …