Machine
A machine is a thermodynamic system that uses power to apply forces and control movement. That definition stretches from a chipped piece of flint to a turbine inside a power plant. It also stretches into your own cells, where biological molecules behave as machines too. The word covers artificial devices driven by engines and motors. It covers natural forces like wind and water. It even covers chemical, thermal, and electrical power feeding mechanisms that shape force into useful output. So how did one idea grow wide enough to hold a hand axe and a robot in the same category? Why did Renaissance natural philosophers settle on six elementary devices as the foundation of everything? And what does it mean that the muscles moving you right now run on machinery measured in nanometers? This is the story of how humans learned to compel the forces of nature to do work.
The hand axe came first, made by chipping flint into a wedge. In a human hand, it turns the force and movement of the tool into a transverse splitting force on the workpiece. The wedge is the oldest of the six classic simple machines, and most machines descend from it. The inclined plane, or ramp, ranks second oldest, used since prehistoric times to move heavy objects.
The wheel and axle was invented in Mesopotamia, modern Iraq, during the 5th millennium BC. The lever mechanism appeared around 5,000 years ago in the Near East, first in a simple balance scale and to shift large objects in ancient Egyptian technology. The lever also drove the shadoof, the first crane machine, which appeared in Mesopotamia around 3000 BC and in Egypt around 2000 BC.
The earliest pulleys date to Mesopotamia in the early 2nd millennium BC and to ancient Egypt during the Twelfth Dynasty, between 1991 and 1802 BC. The screw, last of the simple machines to arrive, first appeared in Mesopotamia during the Neo-Assyrian period, between 911 and 609 BC. The Egyptian pyramids were built using three of the six: the inclined plane, the wedge, and the lever.
Around the 3rd century BC, the Greek philosopher Archimedes studied three of the simple machines, the lever, pulley, and screw. He discovered the principle of mechanical advantage in the lever. Later Greek philosophers defined the classic five simple machines, excluding the inclined plane, and roughly calculated their mechanical advantage.
Hero of Alexandria, who lived from about 10 to 75 AD, listed five mechanisms in his work Mechanics that could set a load in motion: the lever, windlass, pulley, wedge, and screw. He described how they were made and used. Yet the Greeks understood only statics, the balance of forces. They did not grasp dynamics, the tradeoff between force and distance, nor the concept of work.
That gap closed during the Renaissance. In 1586, the Flemish engineer Simon Stevin derived the mechanical advantage of the inclined plane, which was then folded in with the others. In 1600, the Italian scientist Galileo Galilei worked out the complete dynamic theory in Le Meccaniche, or On Mechanics. He was first to understand that simple machines do not create energy. They merely transform it.
Franz Reuleaux, a German mechanician, collected and studied over 800 elementary machines to build a strategy for designing new ones. He saw that the classical simple machines split into two families. The lever, pulley, and wheel and axle are bodies rotating about a hinge. The inclined plane, wedge, and screw are blocks sliding on a flat surface.
The modern approach shifts attention from parts to the connections that allow movement, known as joints. The bearings forming the fulcrum of a lever, and those letting wheels and pulleys turn, are a kinematic pair called a hinged joint. The flat face of an inclined plane or wedge is a sliding joint. The screw gets its own pair, the helical joint.
Reuleaux gave the field a memorable definition. He wrote that a machine is a combination of resistant bodies arranged so the mechanical forces of nature can be compelled to do work with certain determinate motion. Starting from four joint types, the rotary, sliding, cam, and gear joint, plus cables and belts, a machine becomes an assembly of solid parts connecting those joints. Combine two cranks with a connecting link and you get a planar four-bar linkage, the seed of a six-bar linkage or a robot.
Human and animal effort were the original power sources for early machines. Around 300 BC, waterwheels appeared around the world, turning flowing water into rotary motion for milling grain and powering lumber, machining, and textile work. The earliest practical wind machines, the windmill and wind pump, arose in the Muslim world during the Islamic Golden Age, in present-day Iran, Afghanistan, and Pakistan, by the 9th century AD.
Steam came later. The earliest practical steam-powered machine was a steam jack driven by a steam turbine, described in 1551 by Taqi ad-Din Muhammad ibn Ma'ruf in Ottoman Egypt. The word engine itself derives from ingenuity. A steam engine boils water in a pressure vessel so expanding steam drives a piston or turbine, a principle visible in the aeolipile of Hero of Alexandria. Because the heat is added outside the cylinder, it is called an external combustion engine.
An automobile engine burns fuel inside a cylinder, an exothermic reaction, making it an internal combustion engine. A jet engine compresses air with a turbine, burns it with fuel, and expands the gases through a nozzle for thrust. Other sources work differently. Batteries hold chemical potential energy already inside them. Solar cells draw on light and thermoelectric generators on heat, though all of these still require energy to come from elsewhere.
A mechanical system manages power through four parts working together. There is a power source and actuators, a system of mechanisms that shape the input, a controller with sensors comparing output to a goal, and an interface of levers, switches, and displays. Watt's steam engine shows all four. Steam drives the piston, a walking beam and crank turn linear motion into rotation, and the flyball governor controls the steam valve.
Mechanisms are built from machine elements of three basic types. Structural components include frame members, bearings, splines, springs, seals, and fasteners. Mechanisms that control movement include gears and gear trains, cam and follower systems, and linkages. Control components include switches, sensors, actuators, and computer controllers. The recognition that the frame is itself an important element changed the name three-bar linkage into four-bar linkage.
Gears trace back to the Antikythera mechanism of Greece and the south-pointing chariot of China. The involute tooth yielded a standard design with a constant speed ratio. Linkages multiply the possibilities. Watt's linkage generates an approximate straight line and was critical to his steam engine, later reappearing in vehicle suspensions. The Peaucellier linkage produces a true straight line from rotary input. The Klann and Jansen linkages, a six-bar and an eight-bar design, create walking movements.
The earliest programmable machines came from the Muslim world. A music sequencer, a programmable musical instrument, was the first programmable type. The Banu Musa brothers described an automated flute player in their Book of Ingenious Devices in the 9th century. In 1206, Al-Jazari built programmable automata and robots, including four automaton musicians whose drummers ran on a programmable drum machine that could play different rhythms and patterns.
Charles Babbage designed machines in 1837 to tabulate logarithms and other functions. His Difference Engine works as an advanced mechanical calculator, and his Analytical Engine was a forerunner of the modern computer, though none of the larger designs were finished in his lifetime. The Arithmometer and the Comptometer were mechanical computers that preceded digital ones.
Machines also operate inside living cells. The biological molecule myosin reacts to ATP and ADP, engaging an actin filament, changing shape to exert force, then resetting, the molecular drive behind muscle contraction. Kinesin walks along microtubules to transport vesicles, while dynein hauls cargo toward the nucleus and beats motile cilia. As the source puts it, a motile cilium is a nanomachine composed of perhaps over 600 proteins. ATP synthase spins like a turbine to make the cell's energy currency, and researchers have used DNA to build nano-dimensioned four-bar linkages.
Common questions
What is the definition of a machine?
A machine is a thermodynamic system that uses power to apply forces and control movement to perform an action. The term applies to artificial devices such as engines and motors, and also to natural biological macromolecules called molecular machines. Machines can be driven by animals, human power, wind, water, or chemical, thermal, and electrical power.
What are the six simple machines?
The six simple machines are the wedge, the inclined plane, the wheel and axle, the lever, the pulley, and the screw. Renaissance natural philosophers identified these six elementary devices that put a load into motion. The wedge is the oldest, and the screw was the last to be invented.
Where and when were the simple machines invented?
The wheel and axle was invented in Mesopotamia during the 5th millennium BC, and the lever appeared in the Near East around 5,000 years ago. The earliest pulleys date to Mesopotamia in the early 2nd millennium BC and to Egypt during the Twelfth Dynasty, 1991 to 1802 BC. The screw first appeared in Mesopotamia during the Neo-Assyrian period, 911 to 609 BC.
Who discovered the principle of mechanical advantage in the lever?
The Greek philosopher Archimedes discovered the principle of mechanical advantage in the lever around the 3rd century BC. He studied three of the simple machines: the lever, pulley, and screw. Later Greek philosophers defined the classic five simple machines and roughly calculated their mechanical advantage.
Who proved that simple machines do not create energy?
The Italian scientist Galileo Galilei worked out the complete dynamic theory of simple machines in 1600 in Le Meccaniche, or On Mechanics. He was the first to understand that simple machines do not create energy but merely transform it. Earlier Greek understanding had been limited to statics, the balance of forces.
What are molecular machines?
Molecular machines are biological macromolecules that behave like machines inside living cells. Myosin reacts to ATP and ADP to drive muscle contraction, kinesin transports vesicles along microtubules, and ATP synthase spins like a turbine to synthesise ATP. A motile cilium is described as a nanomachine composed of perhaps over 600 proteins.
Who built the earliest programmable machines?
The earliest programmable machines came from the Muslim world. The Banu Musa brothers described an automated flute player, a music sequencer, in their Book of Ingenious Devices in the 9th century. In 1206, Al-Jazari invented programmable automata and robots, including four automaton musicians driven by a programmable drum machine.
All sources
50 references cited across the entry
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