Fulcrums

A fulcrum is the pivot point around which a lever rotates. In a simple lever, a rigid bar rests on a fixed support—the fulcrum—so that a force applied at one point causes a movement of a load at another. The efficiency of a lever depends on the relative distances from the fulcrum to the points where forces are applied, and the system obeys the principle of moments, or torque.

Levers are commonly classified into three classes. In a Class I lever the fulcrum lies between the effort and the load, as in a seesaw or crowbar pivoted on a prop. In a Class II lever the load sits between the fulcrum and the effort, as in a wheelbarrow. In a Class III lever the effort is applied between the fulcrum and the load, as with tweezers or the human forearm when lifting a weight with the hand near the elbow.

Mechanical advantage is the factor by which a lever amplifies the input force and is given approximately by the ratio of the effort-arm length to the load-arm length. A longer effort arm relative to the load arm reduces the required effort but increases movement at the load. The concept also applies to joints and various devices in engineering and biomechanics.

Historically, levers and their fulcrums have been studied since antiquity, notably by Archimedes, and remain foundational in physics, engineering, and design. In measurement devices such as balance scales, a fulcrum provides a stable pivot point for comparing masses.