The nucleus of an atom consists of neutrons, which are uncharged, and protons, which are positively charged. While the uncharged neutrons don’t feel an electrostatic attraction or repulsion to other particles, the positively charged protons should repel each other. In fact, this repulsive force between the protons is quite strong because protons in the same nucleus are very close together. Thus the force that holds them together must be a very strong force. Indeed it is, and it’s even named the strong force. This strong force acts only over distances on the order of 10−15 m—a very very short distance. If the protons were to become separated by a more substantial distance, the strong force would decrease in magnitude faster than the repulsive force, and the protons would be pushed apart. It’s also often said that neutrons act as a sort of “glue” to help bind all of the neutrons and protons together, since there seem to be favored relationships between the number of neutrons and protons present in stable nuclei.
