A lever is a mechanical device used to transmit and transform the effects of forces. The effort and motion is transmitted through the lever to move the load.

The three parts of a lever are the effort, fulcrum, and load. The effort is the input force, the fulcrum is the point around which the lever acts, and the load is the force of the object to be moved.

Lever classes

First order levers position the fulcrum between the effort and the load. The input effort needed can be reduced by moving the fulcrum closer to the load. Examples include scissors, seesaws and crowbars.

Second order levers position the load between the fulcrum and the effort. The input effort needed can be reduced by moving the load closer to the fulcrum. Examples include bottle openers, wheelbarrows, and nutcrackers.

Third order levers position the effort between the fulcrum and load. They do not have a mechanical advantage because the effort is closer to the fulcrum than the load, meaning that the effort is greater than the output. Examples include tweezers, the human arm, and fishing rods.

Linkages

When levers are joined together, they make linkages. Linkages change an input motion and force into a different output motion and force.

Push/Pull Linkages: creates an identical parallel motion at the output.

Bell Crank Linkages: changes the direction of motion through 90 degrees

To change the magnitude of force in a linkage, the pivot must be moved. To make the output force greater than the input force, the pivot is moved closer to the output.