In
particle physics, the
strong interaction is the mechanism responsible for the
strong nuclear force (also called the
strong force,
nuclear strong force), one of the four known
fundamental interactions of nature, the others being
electromagnetism, the
weak interaction and
gravitation. Despite only operating at a distance of a
femtometer, it is the strongest force, being approximately 100 times stronger than electromagnetism, a million times stronger than
weak interaction and 10
38 times stronger than gravitation at that range. It ensures the stability of ordinary matter, confining
quarks into
hadron particles, such as the
proton and
neutron, the largest components of the mass of ordinary matter. Furthermore, most of the
mass-energy of a common
proton or
neutron is in the form of the strong force field energy; the individual quarks provide only about 1% of the mass-energy of a proton.