Simple machines can change the magnitude or direction of a force. Specifically, simple machines are devices that use mechanical leverage to multiply force. They are used in order to maximize the output force to perform certain tasks more efficiently and more easily. The ratio between the input and the output force is known as the mechanical advantage, and it is this advantage that determines the effectiveness of a simple machine.
There are six known simple machines. They are the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw. They are the elementary building blocks that are combined to form more complicated machines. For example, the mechanism of a bicycle includes a pulley, levers, and wheels.
Simple machines can be divided into two categories. The machines in the first category, which are the wheel, the lever, and the pulley, depend on torques equilibrium to perform work. In the second category, machines such as the wedge, the screw, and the inclined plane rely on the vector resolution of force.