Simple machine

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This article is about the concept in physics. For the Internet forum software, see Simple Machines Forum.

Table of simple mechanisms, from Chambers' Cyclopedia, 1728.^[1] Simple machines provide a "vocabulary" for understanding more complex machines.

A simple machine is a mechanical device that changes the direction or magnitude of a force.^[2] In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.^[3] 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:^[4]

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

Simple machines are the elementary "building blocks" of which all more complicated machines (sometimes called "compound machines"^[5]) are composed.^[3][6] For example, wheels, levers, and pulleys are all used in the mechanism of a bicycle. The mechanical advantage of a compound machine is just the product of the mechanical advantages of the simple machines of which it is composed.
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).

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