ZingPath: Simple Machines

A lever is a rod that rotates around a fixed point. The fixed point is called a fulcrum. The work that levers do is called the output force or load. The force being applied to move the lever is called the input force or effort.

Levers have been used by humans for all of recorded history. The famous Greek mathematician Archimedes is given credit for being the first person to define the mathematics of a lever. He was able to show how much levers multiply the input force according to the placement of the fulcrum and distance to the output force.

There are three types of levers. First class levers place the fulcrum between the input force and the output force. An example of this type of lever is a pair of scissors. The handle is where the input force is applied. The blades are where the output force is applied. The fulcrum is the point at which the blades connect to the handle.

A second class lever places the fulcrum at one end of the lever. The input force is applied at the other end of the lever. The output force is in between. A nutcracker is a second class lever. The fulcrum is the hinge at one end. The input force is applied at the other end. The nut is squeezed by the output force.

Third class levers are the only type that does not give any mechanical advantage. In a third class lever the fulcrum is at one end and the output force is at the other end. The input force is applied in the middle. Your arm is an example of a third class lever. The elbow acts as the fulcrum. The fore arm muscles are where the input forces are being applied. Whatever object you are lifting is the output force.