In physics, a simple machine is any device that only requires the application of a single force to work.

The traditional list of simple machines is:

All of these convert low force into high force or vice versa. They may also convert the direction of the force.

The ratio of the input force to the output force is the mechanical advantage. For example, the mechanical advantage of a lever is equal to the ratio of the length of its two arms. The mechanical advantage of an inclined plane (with the force acting parallel to the plane) is the cosecant of the angle of inclination.

Note: Real machines are also affected by factors such as friction and elasticity, so the actual mechanical advantage of a simple machine is will usually differ from its theoretical value.

These simple machines fall into two general classes; those dependent on the vector resolution of forces (inclined plane, wedge, screw, toggle joint) and those in which there is an equilibrium of torques (lever, pulley, wheel). Simple machines are often used in combination as components of more complex machines; for example the Archimedes screw, which is a pump, is an example of a complex machine where the screw is a helical inclined plane.

Variations to the list of simple machines:

  • Some say there are only five simple machines arguing that the wedge is a moving inclined plane.
  • Others further simplify the list to four saying that the screw is a helical inclined plane. This position is less accepted because a screw simultaneously converts a rotational force (torque) to a linear force.

See also

There was also a record label named Simple Machines: http://www.simplemachines.net which closed as of April 1998.