What is the definition of a first-class lever?

A first-class lever is defined as a lever that has its fulcrum positioned between the effort applied and the load that is to be moved. This arrangement allows the lever to change the direction of the applied force. When the effort is applied downward on one side of the lever, the load is lifted upward on the opposite side.

This type of lever is commonly exemplified by a seesaw or a pair of scissors, where the fulcrum allows for movement of two different weights on either end. The key aspect of a first-class lever is that it can amplify force by varying the distances from the fulcrum, which becomes especially useful in lifting heavy loads with less effort. The involvement of the fulcrum between the effort and load is crucial in understanding how first-class levers function and their application in everyday devices.