Momentum and Energy


Who developed gears?

In the first century B.C.E. a Roman merchant ship carrying Greek treasures to Rome sank. In 1900 C.E. a storm caused a party of Greek sponge divers to seek shelter on the island of Antikythera. After the storm passed the divers, seeking sponges, found the wreck of the Roman ship. Over the next nine months they recovered much of the treasure, including a badly corroded block the size of a telephone book. A few months later it fell apart, showing remains of bronze gears, plates covered with scales, and inscriptions in Greek. The German scientist Albert Rehm (1871–1949) understood in 1905 that the device was an astronomical calculator. In 1959 the American historian of science Derek de Solla Price (1922–1983) wrote a Scientific American article describing some of the details of the device and the calculations it could do. By 1974 he had described 27 gears, including the number of teeth on most. By analyzing the teeth he discovered that the ratio could describe lunar cycles known by the ancient Babylonians.

In 2005 Hewlett Packard and X-Tek Laboratories teamed up to produce astonishing images of the device. HP contributed a camera system that used computer enhanced techniques to show inscriptions that were otherwise invisible. X-Tek brought an eight-ton X-ray machine that could produce extremely high resolution 2-D and 3-D images of the internal mechanisms. The X-ray machine also discovered thousands of Greek letters that described details of the mechanisms. They found thirty gears, but analysis suggests that there must have been at least five more to perform the calculations that move dials on the front and back of the box.

The Antikythera device can predict solar and lunar eclipses, the dates of future Olympic games, and can show the complicated motion of the moon. The precision with which the gears were made was greater than any made in the world for the next thousand years. But who made it and where? It is uncertain, but likely to have been made in one of the colonies of Corinth on the island of Sicily, perhaps by a student of Archimedes decades after he was killed in 212 B.C.E.. (See Scientific American, December 2009, and

One method of creating a pulley with a variable diameter is to use a v-shaped belt and a pulley with a groove that can be adjusted in width. This kind of transmission is often used with hybrid cars and is being developed as a means of decreasing fuel use.

As early as 2600 B.C.E. in India and other parts of southern Asia gears were used to open and close doors in temples and to lift water. Around 400 B.C.E. Aristotle (384–322 B.C.E.) described how gears were used. Archimedes described worm gears around 240 B.C.E., and in 40 B.C.E. Vitruvius showed how gears could convert motion from a horizontal axle to a vertical one. In the 1300s C.E. gears were used in clocks in bell towers and on churches.


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