For example, a proton-proton interaction is the same as a The strong force acts only over short distances though, but it does act between all nucleons. So the nuclear strong force is stronger than the electrostatic force. We know that this nucleus is stable, so there must be something else holding the nucleus together, which we call the strong force. And so these two protons are repelling each other, and that's Here's a picture of the nucleus, with two protons and two neutrons, and we know it's stable, even though we know like charges repel. Protons and neutrons in the nucleus are called nucleons, and so I'll use that term a few times in this video. Video, we talked about the helium nucleus, which contains two protons and two neutrons. This is a simplification but it gives you the idea that you cannot think of each particle in isolation. Better to be a repelled proton than an unstable neutron, basically. The overall arrangement becomes more stable once one of those unstable almost-free neutrons becomes a nice, stable proton, even though the proton is repelled by other protons in the nucleus. Something has to give to enable the overall state of the nucleus to become more stable. But remember that free neutrons decay into protons? Well this guy on the outside is not quite free but he's not in a position to be stable. You can sort of imagine there is a neutron on the outside of the nucleus, and if it could get in and be surrounded by more particles, maybe it would be stable. Consider how C-14 decays: one of the neutrons turns into a proton. When you add one more to the pile, even if it will "stick" because of strong nuclear force, it changes the overall arrangement of all the protons and neutrons, and some arrangements are just more stable than others. You have all these particles trying to find a stable arrangement. When you add a neutron to C-13 to get C-14, yes there is more strong nuclear force but you have to consider the nucleus as a whole. They will decay into protons, with a half life of about 10 minutes
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