Simple machine
In
physics, a
simple machine is any device that only requires the application of a single force to work. Work is done when a force is applied and results in movement over a set distance. The work done is the product of the force and the distance. The amount of work required to achieve a set objective is constant, however the force required to do this can be reduced provided the lesser force is applied over a longer distance. Increase the distance and reduce the force. The ratio between the two forces is the mechanical advantage.
The traditional list of simple machines is:
* The
inclined plane (
N)
* The
wheel and axle (
O)
* The
lever (
T)
* The
pulley (
U)
* The
wedge (
V [single wedge];
X [double wedge])
* The
screw (
Y)(The letters are a
mnemonic, because their shapes resemble the shapes of the simple machines.)
The ratio of the output force to the input force is the
mechanical advantage. For example, the mechanical advantage of a lever is equal to the ratio 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 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) 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: wheels, axles, levers, and pulleys are all used in the formation of modern bicycles.
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.
*
Hydraulic and hydrostatic systems are sometimes included.[
1]
*
Machine*
Invention*
Archimedes' screw
