What forces exist between protons and neutrons?
• Two protons of course repel each other electrically, both having the same kind of electric charge, a positive one. • In addition, however, once they get very close to each other, nucleons attract very strongly–and it is this attraction, called the strong nuclear force, that holds them together in a nucleus. There exists another nuclear force, much weaker. What does the weak nuclear force do? • It tries to equalize the number of protons and neutrons inside the same nucleus. If two particles are attracted to each other, and we let their attraction move them–is energy released or absorbed? (if students are not sure) Suppose I hold a stone in my hand–here. The Earth attracts it downwards. If I let it fall in the direction it is attracted–does it gain energy or does energy have to be invested? • It gains energy, that is, energy is released by the process. On the other hand, to lift the stone from the floor against gravity, separating the two attracting objects, you must… ? • … you
