Why is it difficult to get 2 nuclei to fuse together ? ?
Each nuclei is composed of protons and neutrons (except hydrogen that has a single proton). The neutrons have zero charge (they are neutral) but the protons have a positive charge that repels other protons (they can occupy the same nucleus only because the presence of neutrons somehow shield them permitting stability). The protons in the nucleus attract a like number of negatively charged electrons that orbit the atom, making the atom itself neutral. However, when another atom approaches the orbiting electrons repel each other and if the nuclei get very close their protons repel each other in accordance with the inverse square law (where the repelling force grows almost without limit as the distance decreases). This creates a powerful barrier and fusion of hydrogen atoms within the sun occurs randomly only because the tremendous force of enormous pressure squeezes the atoms together and the tremendous heat permits limited numbers of hydrogen atoms enough kinetic energy (of velocity) to
