In particular, the mathematicians investigated equilibrium cases in which the repelling force between any pair of particles is inversely proportional to the distance between them raised to a power. Their formulation is a generalisation of the inverse square law that is well known in physics, where it describes the behavior of forces such as electrical charge and gravity. In their work, the power depends on a parameter labeled s. Hardin and Saff have shown that when s is small, the points act as if they are responding to a long-range force (like gravity or electromagnetism), and when s is large they act as if they are subject to a short-range force (such as the strong force that binds the atomic nucleus together).