Figure 9: Proton force. The interaction energy of two protons is shown as a function of the distance between them. At small separations, the energy is positive and the force is repulsive. At intermediate distances, the nuclear interaction is negative and the force is attractive. At distances larger than shown on the graph, the nuclear force becomes negligible and the repulsive electric force between the two charges is all that is left. The interaction depicted is for protons with antiparallel spins.