Strong Nuclear Force
The Strong Nuclear Force (SNF) is one of the four fundamental forces in the standard model of particle physics together with the electromagnetic force, the weak nuclear force and the gravitation. It is responsible for keeping the neutrons and protons together in the nucleus, outweighing the repulsion between similar charges created by the electromagnetic force.
The SNF affects all particles that are very close to each other. It can only be perceived at distances smaller than 1 femtometer (10−15 meters), which means that it is only perceptible inside the atomic nucleus. The SNF is several orders of magnitude stronger than the rest of the fundamental forces at small scales. However, as soon as the distance between particles is above the femtometer, it has no effect, and other forces like gravity or electromagnetic force are much stronger.