A simple machine is a device that acts to increase or decrease the magnitude of applied force. There are six simple machines: inclined plane, lever, wheel and axle, pulley, wedge, and screw. Energy is conserved in the operation of simple machines and the total work done on a simple machine must equal the total work done by the machine (including work to overcome friction, etc.). Simple machines operate by allowing a trade-off between the magnitude of force and the distance over which that force is applied.

In physics, work is defined as the product of force multiplied by the distance over which the force acts. With regard to simple machines, because the total work done on a system must equal the work output (i.e., the work done by the system) the products of force and distance must always be equal for various force and distance...