Simple machines

July 10th, 2008

In physics and mechanics a simple machine is a mechanical device that changes the direction or magnitude of a force. In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force. A simple machine uses a single applied force to do work against a single load force. Ignoring friction losses, the work done on the load is equal to the work done by the applied force. They can be used to increase the amount of the output force, at the cost of a proportional decrease in the distance moved by the load. The ratio of the output to the input force is called the mechanical advantage.

Usually the term refers to the six classical simple machines which were defined by Renaissance scientists:.

* Lever
* Wheel and axle
* Pulley
* Inclined plane
* Wedge
* Screw

They are the elementary ‘building blocks’ of which all complicated machines are composed. For example, wheels, levers, and pulleys are all used in the mechanism of a bicycle. In the 20th century, a realization that at least one simple machine, the hydraulic press, had been left out, and arguments that some of the six classical devices can be considered as modifications of others (see below), has led some modern sources to avoid specifying any list of simple machines as ‘basic’. Nevertheless, the above six are what is usually meant by ’simple machine’ and are still regarded as the foundation of mechanical technology, although the only reason for preferring this list to others is tradition.

Simple machines fall into two 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).

Entry Filed under: Types