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A lever (/ˈlvər/ or US: /ˈlɛvər/) is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is divided into three types. Also a leverage is a mechanical advantage gained in a mechanical system. It is one of the six simple machines identified by Renaissance scientists. 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. As such, the lever is a mechanical advantage device, trading off force against movement.

Etymology

The word "lever" 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,[1] itself from the adjective levis, meaning "light" (as in "not heavy"). The word's primary 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".[2]

History

The earliest evidence of the lever mechanism dates back to the ancient Near East circa 5000 BC, when it was first used in a simple balance scale.[3] In ancient Egypt circa 4400 BC, a foot pedal was used for the earliest horizontal frame loom.[4] In Mesopotamia (modern Iraq) circa 3000 BC, the shadouf, a crane-like device that uses a lever mechanism, was invented.[3] In ancient Egypt technology, workmen used the lever to move and uplift obelisks weighing more than 100 tons. This is evident from the recesses in the large blocks and the handling bosses which could not be used for any purpose other than for levers.[5]

The earliest remaining writings regarding levers date from the 3rd century BCE and were provided by Archimedes. He stated, 'Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.'

Force and levers

A lever in balance

A lever is a beam connected to ground by a hinge, or pivot, called a fulcrum. The ideal lever does not dissipate or store energy, which means there is no friction in the hinge or bending in the beam. In this case, the power into the lever equals the power out, and the ratio of output to input force is given by the ratio of the distances from the fulcrum to the points of application of these forces. This is known as the law of the lever.[citation needed]

The mechanical advantage of a lever can be determined by considering the balance of moments or torque, T, about the fulcrum. If the distance traveled is greater, then the output force is lessened.