 The biggest difference compared to the gravitational and electromagnetic forces is that the strong nuclear force has a very short range of only a few by 10 to the minus 15 meters. This unit of 10 to the minus 15 meters is so common in nuclear physics that it has been given a special name, the Fermi. Fermi is also a plural, so that instead of saying, for example, 3 by 10 to the minus 15 meters, you can say 3 Fermi. The Fermi is named after Enrico Fermi who set up the first sustained nuclear efficient chain reaction in a squash court at the University of Chicago in 1942. Rembrandt stated that the strong force is the same between all nucleons, either proton-proton, neutron-neutron or proton-neutron. And when I say it has a short range, I really mean that. If nucleons are more than about 5 Fermi apart, there is no strong nuclear force between them. This is very different to the Coulomb force, that, while it gets weaker with distance, never drops to zero until the charged particles are an infinite distance apart. Another peculiarity is that the strong nuclear force becomes repulsive at short distances, so nucleons cannot come really close together. This means nucleons have a sweet spot, and the strong nuclear force prefers to have all of the protons and neutrons in the nucleus being spaced about one Fermi apart. Knowing these facts about the forces between nucleons, we can ask the question, what does this mean for the stability of nuclei?