The seven simple machines are the inclined plane, wedge, screw, lever, pulley, gear and wheel and axis. The simple machines are non-powered mechanical devices that change the direction or magnitude of a force. Each of these machines is considered to be a simple machine. However, when combined, they are considered a complex machine.
Archimedes introduced the idea of simple machines in the third century with the lever, pulley and screw. His work led to the development of the principle of mechanical advantage. Mechanical advantage is the term used to describe the amount of internal force that is used by a mechanical device. When a device takes a small amount of input force and maximizes it, producing a more efficient output, it demonstrates a mechanical advantage. Mechanical advantage allows devices to complete the jobs for which they were designed. After Archimedes, Greek philosophers named four other simple machines: the wedge, gear, wheel and axis. However, it wasn't until 1586, when Simon Stevin was working with the inclined plane and derived the mechanical advantage, that it was recognized as one of the simple machines. Typically, the simple machines are considered as a group of six with the wheel and axis being one category.