A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work. A simple machine is a device that transforms the direction or magnitude of a force.
The word "machine" is derived from the Latin word machina, which in turn derives from the Doric Greek μαχανά (machana), Ionic Greek μηχανή (mechane) "contrivance, machine, engine" and that from μῆχος (mechos), "means, expedient, remedy".
The meaning of machine is traced by the Oxford English Dictionary to an independently functioning structure and by Merriam-Webster Dictionary to something that has been constructed. This includes human design into the meaning of machine.
Historically, a device required moving parts to classify as a machine; however, the advent of electronics technology has led to the development of devices without moving parts that many refer to as machines, such as a computer, radio, and television.
The idea that a machine can be broken down into simple movable elements led Archimedes to define the lever, pulley and screw as simple machines. By the time of the Renaissance this list increased to include the wheel and axle, wedge and inclined plane.
The word engine derives from "ingenuity" and originally referred to contrivances that may or may not be physical devices.
An automobile engine is called an internal combustion engine because it burns fuel (an exothermic chemical reaction) inside a cylinder and uses the expanding gases to drive a piston. A jet engine uses a turbine to compress air which is burned with fuel so that it expands through a nozzle to provide thrust to an aircraft, and so is also an "internal combustion engine." 
Charles Babbage designed various machines to tabulate logarithms and other functions in 1837. His Difference engine is the first mechanical calculator. This machine is considered to be the forerunner of the modern computer though none of them were built in his lifetime.
Study of the molecules and proteins that are the basis of biological functions has led to the concept of a molecular machine. For example, current models of the operation of the kinesin molecule that transports vesicles inside the cell as well as the myocin molecule that operates against actin to cause muscle contraction; these molecules control movement in response to chemical stimuli.
Researchers in nano-technology are working to construct molecules that perform movement in response to a specific stimulus. In contrast to molecules such as kinesin and myosin, these nano-machines or molecular machines are constructions like traditional machines that are designed to perform in a task.
Perhaps the first example of a human made device designed to manage power is the hand axe, made by chipping flint to form a wedge. A wedge is a simple machine that transforms lateral force and movement of the tool into a transverse splitting force and movement of the workpiece.
Machines are assembled from components called machine elements. These elements consist of mechanisms that control movement in various ways such as gear trains, transistor switches, belt or chain drives, linkages, cam and follower systems, brakes and clutches, and structural components such as frame members and fasteners.
Modern machines include sensors, actuators and computer controllers. The shape, texture and color of covers provide a styling and operational interface between the mechanical components of a machine and its users.
Assemblies within a machine that control movement are often called "mechanisms."   Mechanisms are generally classified as gears and gear trains, cam and follower mechanisms, and linkages, though there are other special mechanisms such as clamping linkages, indexing mechanisms and friction devices such as brakes and clutches.
For more details on mechanical machines see Machine (mechanical) and Mechanical systems.
Controllers combine sensors, logic, and actuators to maintain the performance of components of a machine. Perhaps the best known is the flyball governor for a steam engine. Examples of these devices range from a thermostat that as temperature rises opens a valve to cooling water to speed controllers such the cruise control system in an automobile. The programmable logic controller replaced relays and specialized control mechanisms with a programmable computer. Servomotors that accurately position a shaft in response to an electrical command are the actuators that make robotic systems possible.
Machine design plays an important role in all three of the major phases of a product lifecycle:
- invention, which involves the identification of a need, development of requirements, concept generation, prototype development, manufacturing, and verification testing;
- performance engineering involves enhancing manufacturing efficiency, reducing service and maintenance demands, adding features and improving effectiveness, and validation testing;
- recycle is the decommissioning and disposal phase and includes recovery and reuse of materials and components.
- Darwin Among the Machines
- History of technology
- Human body
- ^ a b The American Heritage Dictionary, Second College Edition. Houghton Mifflin Co., 1985.
- ^ "μηχανή", Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus project
- ^ "μῆχος", Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus project
- ^ Oxford English Dictionary
- ^ Merriam-Webster Dictionary Definition of machine
- ^ "Internal combustion engine", Concise Encyclopedia of Science and Technology, Third Edition, Sybil P. Parker, ed. McGraw-Hill, Inc., 1994, p. 998 .
- ^ Reuleaux, F., 1876 The Kinematics of Machinery, (trans. and annotated by A. B. W. Kennedy), reprinted by Dover, New York (1963)
- ^ J. J. Uicker, G. R. Pennock, and J. E. Shigley, 2003, Theory of Machines and Mechanisms, Oxford University Press, New York.
- Oberg, Erik; Franklin D. Jones, Holbrook L. Horton, and Henry H. Ryffel (2000). ed. Christopher J. McCauley, Riccardo Heald, and Muhammed Iqbal Hussain. ed. Machinery's Handbook (26th edition ed.). New York: Industrial Press Inc.. ISBN 0-8311-2635-3.
- Reuleaux, Franz; (trans. and annotated by A. B. W. Kennedy) (1876). The Kinematics of Machinery. New York: reprinted by Dover (1963).
- Uicker, J. J.; G. R. Pennock and J. E. Schigley (2003). Theory of Machines and Mechanisms. New York: Oxford University Press.
Wikimedia Foundation. 2010.