What best defines the nuclear force?

• A. The attractive, short-range force among nucleons.
• B. The repulsive force between protons at all distances.
• C. The long-range electromagnetic force between charged particles.
• D. The force that binds electrons to the nucleus.

Answer: (A)

The strong nuclear force is an attractive interaction between nucleons that acts over a very short range to hold the nucleus together. It binds protons and neutrons, overcoming their electrostatic repulsion, because it is strongest at distances of about a femtometer and quickly becomes negligible beyond a couple of femtometers. Realistic nucleon-nucleon forces even have a repulsive core at extremely short separations, but within the typical nuclear distances the net effect is attraction, which is why nuclei remain bound. Importantly, this force is effectively the same for proton-proton, neutron-neutron, and proton-neutron pairs when electromagnetic effects are set aside, reflecting its charge-independence at the nuclear scale. It isn’t the electromagnetic force, which is long-range and governs interactions between charged particles and the binding of electrons to the nucleus.