Scientists often think about the two ways the strong interaction works as separate forces: the colour force and the nuclear force. At distances of 0.8 fm and less, the colour force holds subatomic particles like protons and neutrons together. At distances of 1 to 3 fm, the residual (leftover) strong force is what keeps protons and neutrons together in the atomic nucleus, so it is called the nuclear force. (This is like thinking of electricity and magnetism as separate forces, when the fundamental force is electromagnetism.)