For nuclear fusion to take place, a large amount of energy is needed. With this energy, the atoms are pushed together, which are repelled by the electrostatic force (a force between protons which are particles in the nucleus of the atom and have a positive electrical charge). But once this force is overcome and the nuclei are pushed close enough together, another much more powerful force will take over: the strong nuclear force. It only operates at short distances, so when the nuclei are close enough, they attract each other because of the strong nuclear force which is stronger than the electrostatic force. It is hoped that the energy released by cold fusion is much greater than the energy used to push the atoms together.