What Is a Lever

A lever is a rigid bar or rod that can pivot about a fixed position. This fixed position is called a fulcrum. Examples of levers include a seesaw, a crowbar, and a bottle opener. A lever is a type of simple machine. When a person does work on a machine, he or she is transferring energy to the machine. The amount of work done can be calculated by multiplying the magnitude of the force acting on an object by the distance the object moves. The work a person does on a machine is called the input work and the work done by the machine is called the output work. The output work can never be greater than the input work. The machine does not add energy to the system; it simply transfers energy in an efficient way. The force the person exerts on the lever in order to perform work is called the effort force. The force that the lever exerts on an object, performing work, is called the resistance force. For example, if a screwdriver is used to pry the lid off a paint can, the force exerted by the person on the screwdriver is the effort force and the force the screwdriver exerts on the can is the resistance force. Levers can be divided into three classes, based on the location of the fulcrum. First-class levers are those where the fulcrum is between the effort force and the resistance force. Examples of first-class levers include a crowbar or a seesaw. Second-class levers are those where the fulcrum is at the end of the bar or rod. These levers also multiply the effort force applied by decreasing distance; however, the direction of the force is not changed. Examples of second-class levers include a wheelbarrow or a bottle opener. Third-class levers are those where the fulcrum is at the same end as the effort force. In these levers, the resistance distance is actually greater than the effort distance. Third-class levers reduce effort force by increasing the resistance distance, so even though they do not multiply force, they still ease a load. Examples of third-class levers...