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.
Simple machines are the basic components of complex machines, such as a bicycle or an automobile. A machine is used to ease a load. Simple machines include the lever, wheel and axle, pulley, inclined plane, wedge, and screw. These machines can change the strength or direction of a force in order to do work. When a person does work on a machine, he or she is transferring energy to the machine. The machine then uses that energy to perform work on another object. The machine, therefore, transfers its energy to the object. Work is performed whenever a force moves an object. 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.
When an effort force is applied to a lever, the lever overcomes the resistance force by pivoting on the fulcrum. In the above example, a person pushes down on the screwdriver, and the screwdriver pivots on its fulcrum, pushing the paint can lid up. In other words, the lever changes the direction of the force. The distance the screwdriver moves down (the effort distance) is greater than the distance the lid moves up (the resistance distance). Ideally, the work done by the screwdriver on the lid is equal to the work done by the person on the screwdriver. Since work is force times distance, and the amount of work is conserved, if the effort distance is greater than the resistance distance, the effort force must be smaller than the resistance force. In other words, the lever multiplies the effort force, easing a load.
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 include hammers, tweezers, and fishing poles. Regardless of type, all levers perform work on an object in order to ease a load.
This is the complete article, containing 600 words
(approx. 2 pages at 300 words per page).
