Lever
From prehistoric times levers were used for cultivation, excavation, and moving large objects. Such implements as hoes, slings, and oars were conceived and constructed to enhance human effort. The key to their operation is the relative positions of the load, the pivot called a fulcrum, and the applied effort. To maximize the applied effort, the most effective placement of the fulcrum was found to be close to the load.
As early as 5000 B.C. a simple balance scale employing a lever was used to weigh gold and other items. A Greek device called a steelyard improved on these simple scales by adding a sliding weight to enhance precision. Around 1500 B.C., the shaduf, a forerunner of the crane, made its appearance in Egypt and India as a device for lifting containers of water.
Scholars of this period may well have provided suitable explanations for the mechanics of the lever, but it was left to Greek theoretician Archimedes in the third century B.C. to document the underlying relationships between force, load, and distance from the fulcrum point. Archimedes' law of levers survives in the law of equilibrium, which states, "effort multiplied by the length of the effort arm equals the load multiplied by the length of the load arm, where the effort arm equals the distance from the fulcrum to the point of applied effort and where the load arm equals the distance from the fulcrum to the center of the load weight."
Simply put, this means that the longer the effort end of the lever the less force that is needed. (Today we say that the torques on each end of the lever are equal.) What is most important is the mechanical advantage--the reduction in pounds of effort versus pounds of load--that is gained.
Archimedes' law, which was expanded by Hero of Alexandria, applies to all types of levers. It should be noted that levers exist where the fulcrum rests beyond the load (e.g., the wheelbarrow, with the wheel serving as a fulcrum) or beyond the effort (in the case of tongs, with the elbow joint serving as a fulcrum).
In 1743 John Wyatt (1700-1766) introduced the concept of the compound lever, which consists of two or more levers working together to further reduce effort. A modest everyday example of a compound lever is a nail clipper.
The principle that underlies the movement of levers is the same as that which governs inclined planes, pulleys, cranes, gears, and belts. Although levers are often taken for granted, they are a singularly important tool class and are incorporated in countless common objects. Crowbars, nutcrackers, seesaws, scissors, hammers, pliers, and bottle openers would all be unthinkable without the concept of the lever.
This is the complete article, containing 443 words
(approx. 1 page at 300 words per page).
