A simple machine consisting of a rigid bar pivoted about a fulcrum. The mechanical advantage or force ratio of a lever (the ratio of load to effort) is equal to the ratio of the perpendicular distance of the line of action of the effort from the fulcrum to the perpendicular distance of the line of action of the load from the fulcrum. In a first-order lever the fulcrum comes between load and effort. In a second-order lever the load comes between the fulcrum and the effort. In a third-order lever the effort comes between the fulcrum and the load.
Levers.
A rigid bar or rod free to rotate about a point or axis, called the fulcrum, normally used to transmit a force at one point to a force at another. In diagrams the fulcrum is usually denoted by a small
triangle. In the three examples shown in the figure, the lever is being used as a machine in which the effort is the force P and the load is W. In each case, the mechanical advantage can be found by using the principle of moments. Everyday examples corresponding to the three kinds of lever shown are (i) an oar as used in rowing, (ii) a stationary wheelbarrow, and (iii) the jib of a certain kind of crane.