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lever
A lever ( or ) is a machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. It is one of the six simple machines identified by Renaissance scientists. The word entered English about 1300 from Old French, in which the word was ''levier''. This sprang from the stem of the verb ''lever'', meaning "to raise". The verb, in turn, goes back to the Latin ''levare'', itself from the adjective ''levis'', meaning "light" (as in "not heavy"). The word's ultimate origin is the Proto-Indo-European (PIE) stem ''legwh-'', meaning "light", "easy" or "nimble", among other things. The PIE stem also gave rise to the English word "light".〔(Etymology of the word "lever" in the Online Etymological Dictionary )〕 A lever amplifies an input force to provide a greater output force, which is said to provide leverage. The ratio of the output force to the input force is the mechanical advantage of the lever.
==Early use==
The earliest remaining writings regarding levers date from the 3rd century BC and were provided by Archimedes. 'Give me a place to stand, and I shall move the Earth with it' is a remark of Archimedes who formally stated the correct mathematical principle of levers (quoted by Pappus of Alexandria). The distance required to do this might be exemplified in astronomical terms as the approximate distance to the Circinus galaxy (roughly 3.6 times the distance to the Andromeda Galaxy) - about 9 million light years.
It is assumed that in ancient Egypt, constructors used the lever to move and uplift obelisks weighing more than 100 tons.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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