How do you know how strong interaction forces are?

Protons and neutrons are bound together in an atomic nucleus by the strong interaction, which must overcome the electromagnetic force that is causing the positively charged protons to repel one another.

The masses of free protons and neutrons are known. The mass of an atomic nucleus is less than the total of the masses of the equivalent number of free protons and neutrons. This difference in mass is known as the mass deficit or binding energy. The binding energy per nucleon, which is a measure of the strong interaction's strength, is obtained by dividing the mass difference by the total number of nucleons.

The mass of a proton is 1.007825 amu, while the mass of a neutron is 1.008665 amu.

Since the mass of a Helium-4 nucleus is 4.002602 amu, each nucleon has a binding energy of 0.0075945 amu. Because Helium-4 is very stable, it is found in large quantities.

With a mass of 61.928345 amu and a binding energy per nucleon of 0.00944137, Nickel-62 is the element with the highest binding energy per nucleon.

For elements heavier than nickel, each proton in the nucleus repels every other one, but the strong interaction only binds nucleons to their neighbors. Heavier elements need more neutrons to be stable. For example, compare Uranium-238, which has 146 neutrons and 92 protons, with Nickel-62, which has 34 neutrons and 28 protons. Uranium-238 is the most common isotope of uranium and is radioactive. Its binding energy per nucleon is 0.0081269.

The strength of interaction forces is typically determined by observing the magnitude of the forces between particles or objects, as well as analyzing the behaviors of these particles or objects under the influence of the forces.