Archimedes’ principle describes a law of physics regarding how fluids interact with a solid body in their midst. It is, basically, the concept of buoyancy: A body immersed in liquid will be subject to upward forces equal to the fluid it displaces. This upward force is known as buoyancy, and it is what keeps ships, people and objects afloat.
In addition to being an early discovery in the study of physics, Archimedes’ principle also spawned a colorful story that is still told more than two millennia later. No contemporary accounts of Archimedes’ life survive, and this story may well have been created by fanciful historians of the Roman era. Galileo, writing in 1586, proposed that Archimedes could well have achieved the same result with a slightly more scientific method.
Archimedes lived in Syracuse, a Greek colony in Italy, in the third century B.C. He was one of the greatest scientists of ancient times, working in both theoretical and applied sciences. He invented devices for science and war and discovered the basic principles of mathematical calculus. While his inventions were better known than his theories during his lifetime, the reverse is true in modern times. The discovery of Archimedes’ principle is one of the best-known stories about this great thinker.
According to a legend recounted by the Roman historian Vitruvius, the king of Syracuse challenged Archimedes to discover whether a crown was truly composed of solid gold, or if other metals had been added, as he suspected. Archimedes spent some time considering the problem, because he could not melt down or otherwise damage the crown to analyze its composition. The solution came to him in a flash as he was settling into a full bath and realized the water displaced from the tub was equal to the mass of his body. In a moment of inspiration, it is said, he knew he could solve the problem by immersing the crown. If it displaced less water than an equivalent quantity of gold, it contained other metals.
Archimedes is said to have been so elated by this discovery that he left his house, racing naked through the streets of Syracuse shouting, “Eureka!” This Greek word means “I have found it,” and is still used in modern times to denote a moment of enlightenment or discovery. The popular legend of Archimedes’ principle illustrates, and may have helped to establish, the common perception of the absent-minded scientist who values knowledge and theory over social niceties such as clothing.