What holds the nucleons within the nucleus? Why don't 2 positively charged protons repel each other out of the nucleus? These questions are answered by indicating that there is a stronger force existing in the nucleus, stronger than gravity and stronger than the electromagnetic force between nucleons. This force is called the strong nuclear force. Discuss facts regarding the strong force and how it acts. Indicate that energy must be added to a nuclear system in the form of work in order to remove nucleons from the nucleus. Discuss that the energy of the assembled nucleus is less than the sum of the energy of each individual nucleon, and the difference is called the binding energy.