ABSTRACT
A "simple" machine is a device used to increase force, to increase speed, or to change the direction of a force. There are only six simple machines: lever, pulley, wheel and axle, inclined plane, wedge, and screw. A lever is a rigid bar, straight or curved, with a pivot or fulcrum at some point along its length so that a force acting at one point can apply a much larger force at a different point along the lever. A pulley consists of a wheel which is free to turn on its axle and carries a rope, cable, or belt. A wheel and axle consists of a wheel attached to a smaller-diameter shaft or axle which turns with the wheel. A screw is sometimes described as an inclined plane wrapped around a cylinder. By using a screw, it is possible to generate a large force along the axis of the screw by applying a relatively small moment to the screw.
