Simple machines can change the magnitude or direction of a force. Specifically, simple machines are devices that use mechanical leverage to multiply force. By maximizing the output force that is created by the leverage, certain tasks perform 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: those that rely on torques equilibrium and those that rely on the vector resolution force. The machines in the first category are the wheel, lever, and pulley while the wedge, screw, and inclined plane lie in the second group.