Review alpha and beta particles and gamma rays. Discuss the nuclear strong force between protons and neutrons. Determine that the force acts over a short distance, about the radius or a proton. Elicit that the force holds the protons and neutrons in the nucleus. Determine that work must be done to remove a nucleon from the nucleus, which requires energy to do the work. Elicit that the total energy of the nucleus, the assembled energy, is less than the sum of the energy of the nucleons. The difference is the binding energy of the nucleus. Develop that according to Einstein, the mass and energy are two sides of the same coin, and energy is determined from E=mc^2.