All levers are made up of three parts: (1) fulcrum—the pivot around which the lever revolves; The force applied to the lever is referred to as the input force (also known as the effort). The output force (also known as the load) is the force exerted by the lever in order to move the load. Levers are classified into three types: first class, second class, and third class. In first class levers, both ends are rigid; in second class levers, one end is rigid while the other is hinged; in third class levers, both ends are hinged. The point where a fourth-class lever meets the ground is called the tip of the lever. All other points on the lever beyond the tip are called shoulders. On a fourth-class lever, the shoulders cannot support any weight be it from man or beast. A fourth-class lever can be used by itself as an extension of your arm for lifting small objects. It can also be used as a means of supporting a weight supported by another object with more strength than you have. For example, if someone has enough strength to lift a car off of a person then that person could use a fourth-class lever to lift the car. A third-class lever needs two shoulders to function properly. One must be strong enough to support a weight equal to or greater than the effort applied to it. If not, the lever will collapse.