In particle physics, the strong interaction (Strong Force) is one of the four fundamental interactions of nature, the others being electromagnetism, the weak interaction and gravitation. It is a non-contact force. At atomic scale, it is about 100 times stronger than electromagnetism, which in turn is orders of magnitude stronger than the weak force and gravitation.
The strong interaction is observable in two areas: On the larger scale, it is the force that binds protons and neutrons together to form the nucleus of an atom. On the smaller scale, it is also the force that holds quarks and gluons together to form the proton, the neutron and other particles. (source: wiki)
During particle collisions it is hard to find out if protons and neutrons would all be located in a center nucleus or in a structured disperse setting, as the center of mass for both settings is ... in the middle.
Atomic models: http://en.wikipedia.org/wiki/Geiger-Marsden_experiment