How do protons and neutrons interact in an atomic nucleus?

Protons and neutrons interact in an atomic nucleus primarily through the strong nuclear force. This fundamental force is one of the four known fundamental forces of nature and is responsible for holding the protons and neutrons together within the nucleus, despite the electromagnetic repulsion that would occur between protons due to their positive charges.

The strong nuclear force operates at very short ranges—typically about the size of a nucleus—and is much stronger than the electromagnetic force at these distances. It helps to overcome the repulsion between the positively charged protons and ensures the stability of the nucleus. Without the strong nuclear force, nuclei would not be able to exist, as the repulsive forces between protons would cause them to fly apart.

While the weak nuclear force is responsible for certain types of radioactive decay and interactions involving neutrinos, it does not contribute significantly to the stability of the nucleus. Similarly, gravitational attraction has a negligible effect at the scale of atomic particles due to their relatively small masses compared to the forces at play within the nucleus. Thus, the strong nuclear force is the defining interaction that allows protons and neutrons to coexist in atomic nuclei.