The early work by Fermi and others was presented as an introduction into nuclear fission. The process of bombarding a uranium nucleus by a neutron was shown, and the reason why this caused the electric force of repulsion in the nucleus to overcome the nuclear strong force shown in a diagram. The equation for the fission of U-235 was written, showing the products formed and the formation of 3 additional neutrons released, which then bombarded 3 additional U-235, starting a chain reaction.