A simple machine is an elementary device that has a specific movement, which can be combined with other devices and movements to form a machine. Usually the term refers to the six classical simple machines, which were defined by Renaissance scientists as lever, wheel and axle, pulley, inclined plane, wedge, and screw. A simple machine has an applied force that works against a load force. If there are no friction losses, the work done on the load is equal to the work done by the applied force. This allows an increase in the output force at the cost of a proportional decrease in the distance moved by the load. The ratio of the output force to the input force is the mechanical advantage of the machine.