lever

A lever is a rigid bar that pivots around a fixed point called a fulcrum. It is one of the six classical simple machines and is used to multiply force or change its direction. By applying an effort at one point along the bar, the lever transmits torque to a load at another point, enabling the user to raise or move a heavy object with less input force.

The lever operates according to the principle of moments. At equilibrium, the product of the effort force (F_e) and its distance from the fulcrum (d_e) equals the product of the load force (F_l) and its distance from the fulcrum (d_l): F_e d_e = F_l d_l. The mechanical advantage MA is the ratio F_l/F_e and equals d_e/d_l. When the distance from the fulcrum to the effort is greater than that to the load, the lever provides a force advantage; if the distances are equal, no amplification occurs; if the effort is closer, the lever trades force for speed and range of motion.

There are three classes of levers, distinguished by the position of the fulcrum relative to the load and effort. In a first-class lever, the fulcrum lies between load and effort (examples: seesaw, crowbar). In a second-class lever, the load is between the fulcrum and the effort (examples: wheelbarrow). In a third-class lever, the effort is between the fulcrum and the load (examples: tweezers, many bicycle hand levers).

Historically, levers have been used since ancient times and were described by Archimedes as a means to move heavy weights. In practice, they enable lifting, prying, cutting, and handling loads, often with a trade-off between force, distance, and speed. Friction, deformation, and material limits limit real-world performance.