The Strong Nuclear Force

The nucleus contains positively charged protons, which repel each other electrostatically. The gravitational attraction between nucleons is far too weak to hold the nucleus together. Instead, a much stronger force acts: the strong nuclear force.Properties of the strong nuclear force:• It acts between all hadrons (such as protons and neutrons) and between the quarks inside them. It does not act on leptons such as electrons.
• It acts equally between proton-proton, proton-neutron and neutron-neutron pairs.
• It has a very short range. It is attractive up to a separation of about 3 fm (3 × 10⁻¹⁵ m), and beyond that it quickly becomes negligible.
• At separations less than about 0.5 fm it is repulsive, which stops nucleons being pulled into each other.Because of its short range, each nucleon only attracts its nearest neighbours. The electrostatic repulsion between protons, however, has an infinite range and acts across the whole nucleus. This is why very large nuclei become unstable.Example: two protons 2 fm apart feel both the strong attraction and the electrostatic repulsion. The strong force is much larger, so the resultant force is attractive. At 10 fm apart, the strong force is negligible and only the electrostatic repulsion acts.