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The compound lever is a simple machine operating on the premise that the resistance from one lever in a system of levers will act as power for the next, and thus the applied force will be amplified from one lever to the next (as long as the mechanical advantage for each lever is greater than one). Almost all scales use some sort of compound lever to work. Other examples include nail clippers and piano keys. ==Mechanical advantage== A lever arm uses the fulcrum to lift the load using and intensifying an applied force. In practice, conditions may prevent the use of a single lever to accomplish the desired result,〔Popular Mechanics magazine, April, 1924, p. 615-617〕 e.g., a restricted space, the inconvenient location of the point of delivery of the resultant force, or the prohibitive length of the lever arm needed. In these conditions, combinations of simple levers, called compound levers, are used. Compound levers can be constructed from first, second and/or third-order levers. In all types of compound lever, the rule is that force multiplied by the force arm equals the weight multiplied by the weight arm. The output from one lever becomes the input for the next lever in the system, and so the advantage is magnified. The figure on the left illustrates a compound lever formed from two first-class levers, along with a short derivation of how to compute the mechanical advantage. With the dimensions shown, the mechanical advantage, W/F can be calculated as = 7.5, meaning that an applied force of 1 pound (or 1 kg) could lift a weight of 7.5 lb (or 7.5 kg). Alternatively, if the position of the fulcrum on lever AA' were moved so that A1 = 4 units and A2 = 9 units, then the mechanical advantage W/F is calculated as = 1, meaning that an applied force will lift an equivalent weight and there is no mechanical advantage. This is not usually the goal of a compound lever system, though in rare situations the geometry may suit a specific purpose. The distances used in calculation of mechanical advantage are measured perpendicular to the force. In the example of a nail clipper on the right (a compound lever made of a class 2 and a class 3 lever), because the effort is applied vertically (that is, not perpendicular to the lever), distances to the respective fulcrums are measured horizontally, instead of along the lever. In this example, W/F is = 6. Note that (7 + 1) cm = 8 cm is the distance from the point of application of the effort to the fulcrum of the first lever, perpendicular to the applied effort. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「compound lever」の詳細全文を読む スポンサード リンク
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