Summary
Highlights
A machine is any device that uses energy to do work. Work, in science, is defined as a force exerted over a distance. For example, lifting a 1-newton apple by 1 meter equates to 1 joule of work.
Complex machines like bicycles are composed of simpler parts. These fundamental components are called simple machines. The six generally recognized simple machines, dating back to da Vinci's time, are the lever, wheel and axle, pulley, inclined plane, wedge, and screw. A simple machine changes the direction or magnitude of a force.
All simple machines can be categorized into two basic types: the lever or the inclined plane. The wheel and axle, and pulley are variations of the lever, while the wedge and screw are variations of the inclined plane.
A lever consists of an arm and a fulcrum. An input force (Fi) is applied on one side, resulting in an output force (Fo) on the other. Mechanical advantage is the ratio of output force to input force (Fo/Fi), indicating how much a lever magnifies the input force. While a lever can magnify force, it requires applying that force over a greater distance, meaning work input equals work output.
The inclined plane is the second fundamental type of simple machine. While it can reduce the force needed to move an object vertically (like stairs making it easier than a ladder), it requires moving the object over a greater distance. This often leads to more work input than work output due to friction, which introduces the concept of efficiency. A 100% efficient machine, where input and output work are identical, does not exist in reality.