fulcrum

A fulcrum is the fixed point around which a lever pivots. It serves as the support point on which the lever balances and rotates, enabling a small input force to produce a larger output force or motion. The word comes from Latin fulcrum, meaning "support, prop." The term is often used in physics and engineering to describe the pivot or support point of a lever, but in everyday usage it may refer more generally to any point of balance.

In static lever systems, the torques about the fulcrum must balance. If a force F1 is applied at a distance r1 from the fulcrum on one side and a force F2 is applied at distance r2 on the other, equilibrium requires F1*r1 = F2*r2, with direction considered. The ratios of distances define the lever's mechanical advantage: MA = r1/r2 (for appropriate configurations). The three classic lever classes are defined by the location of the fulcrum relative to the load and effort.

First-class lever: fulcrum between effort and load (seesaw). Second-class: load between fulcrum and effort (wheelbarrow). Third-class: effort between fulcrum and load (human forearm). Levers are among the six simple machines defined by Renaissance scientists and are used to amplify force or distance.

Beyond simple machines, the term fulcrum appears in biomechanics, architecture, and other domains to denote any central point of support or balance. In mechanical systems, a fulcrum is typically realized by a fixed pivot, bearing, or support point.