The strong nuclear force holds the particles of an atom's nucleus together. The subatomic particles affected by the strong force are called nucleons and consist of protons and neutrons.
The strong force is one of the four fundamental forces found in nature along with gravity, the electromagnetic force and the weak nuclear force. It is the strongest of the four and is responsible for preventing positively charged protons from repelling each other. It also has the shortest range of the four and only affects particles that are very close together.
The strong force works by exchanging smaller particles called mesons back and forth between nucleons. If the distance between nucleons becomes too large, the strong force is ineffective and other forces, such as electromagnetism, can pull the particles apart.