strong interactions, actions between elementary particles mediated, or carried, by gluons. They are responsible for the binding of protons and neutrons in the nucleus and interactions between quarks. Quantum field theory applied to the understanding of these strong interactions is called quantum chromodynamics (QCD). Strong interactions are one of four fundamental interactions in nature, the others being gravitation, electromagnetism, and the weak interactions.

Strong, William Duncan, 1899-1962, American anthropologist, b. Portland, Oreg., grad. Univ. of California (B.A., 1923; Ph.D., 1926). He served as curator at the Chicago Field Museum (1926-29) and as senior anthropologist at the Bureau of American Ethnology (1931-37) and taught at the Univ. of Nebraska (1929-31) and at Columbia (1937-62). Trained in both archaeology and ethnography, Strong was a proponent of using ethnographic and historical sources in the interpretation of archaeological remains. He conducted research in Labrador, the Great Plains, Honduras, and Peru. His writings include An Introduction to Nebraska Archeology (1935), Cultural Resemblances in Nuclear America (1951), and Cultural Stratigraphy in the Viru Valley, Northern Peru (with Clifford Evans, 1952).

Smith, Jedediah Strong, 1799-1831, American explorer, one of the greatest of the mountain men, b. near Binghamton, N.Y. Early in 1824, Smith took a party through South Pass, beginning the regular use of that route. He and a few men headed north and into present-day Montana and as far north as the Canadian boundary before going back to Great Salt Lake. In 1825 he set out from Great Salt Lake on his most famous journey. Traveling southwest with a small band of men, he crossed the Colorado River and the Mojave Desert, arriving in San Diego, Calif., then part of Mexico. In 1831, Smith set out from St. Louis with a company on the Santa Fe Trail and was killed along the Cimarron River by Comanches. His wide travels opened not only the rich fur-trapping and trading country but also trails and territory that were soon frequented by westward-bound American pioneers. His journal was edited by Maurice Sullivan (1934).

Robert the Strong, d. 866, French warrior, marquess of Neustria; father of the French kings Eudes and Robert I and ancestor of the Capetians. He joined the rebellious nobles against Charles II, Emperor of the West. They invited Louis the German to invade France (858). Becoming reconciled to Charles in 861, Robert was charged with the defense of the country between the Seine and the Loire, from which he repelled the Bretons and the Normans. He was killed fighting against the Normans.

or strong nuclear force

Fundamental force acting between elementary particles of matter, mainly quarks. The strong force binds quarks together in clusters to form protons and neutrons and heavier short-lived particles. It holds together the atomic nucleus and underlies interactions among all particles containing quarks. In strong interactions, quarks exchange gluons, carriers of the strong force, which are massless particles with one unit of intrinsic spin. Within its short range (about 10⁻¹⁵ m), the strong force appears to become stronger with distance. At such distances, the strong interaction between quarks is about 100 times greater than the electromagnetic force.

Learn more about strong force with a free trial on Britannica.com.