What is a simple machine?

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. Usually the term refers to the six classical simple machines that were defined by Renaissance scientists: (From Wikipedia)

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

Mechanical advantage

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. The machine can 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 applied force is called the mechanical advantage. (From Wikipedia)

Building blocks

Simple machines can be regarded as the elementary “building blocks” of which all more complicated machines (sometimes called “compound machines” are composed. 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. (From Wikipedia)