100 Best Books for an Education

A Revision and Update of Will Durant's 100 Best Books for an Education

Note 18

 The Wonderful World of Machinery



What is a machine?


The world is filled with innumerable tasks that need to be done. From a physicist’s perspective, these tasks require us to perform work. But what is work? Mathematically,


Work (W) = Force (F) · Distance (D) against resistance


and the rate of doing work is mathematically equal to the rate of using energy.


F = Mass (M) · Acceleration (A).


“A” is the rate of change in motion—whether the change involves speed, direction, or both. Therefore, a force can also cause a change in an object’s direction of motion.


D = Velocity (V) · Time (T)


where V is defined as uniform speed and direction per unit time, so D = V/T · T. Therefore, for our purposes D and V are equal.

    A machine is any device that makes work easier; it produces (by transforming one form of motion/energy into another) or transmits an effort (input force) and changes the direction/decreases the amount of force required to do a given amount of work (output force) to overcome the resistance of a load. Mathematically then all machines are:


F · D (input) = F · D (output)


if we lower one term, its mirror opposite must correspondingly be increased and the remaining three terms must change if any one of them changes.   

    Essentially a machine functions as a processor or converter where the movement of the input entirely controls the movement of the output through a kinematic linkage but it is modified in some fashion. The ratio of the output load to the input effort is the machine’s mechanical advantage (MA)—and it is crucial to understanding the functioning of a machine. Less crucial is the machine’s velocity ratio (VR) or the ratio of the motion distance/velocity of the effort to the motion distance/velocity of the load. In an ideal machine if we multiply the mechanical advantage by the velocity ratio it must equal one i.e. a trade-off exists between force and speed. An infinitesimal motion in one direction or the other can move an ideal machine (when the effort and load are in equilibrium) making the machine fully reversible. In a real machine, the product of MA and VR is inevitably less than one due to losses from friction. A real machine, therefore, needs a certain effort to overcome friction and move it in either direction and there is an inevitable loss of energy when it moves.

    Although the load force can be many times greater than the effort force, the total output energy/work can never exceed the total input energy/work. In principle work input = work output. However, due to friction the useful work done by a machine is always less than the input work put into it. The percentage of the effective work performed by a machine and input work put into the machine multiplied by 100% is the efficiency of that machine. Thus in practice the efficiency is always less than 100% in accord with the law of conservation of energy. The inability to lower friction to zero prevents the creation of a perpetual motion machine. The force necessary to overcome friction is proportional to the absolute perpendicular force pushing one surface against another i.e. when we slide an object across a surface and then double its mass, the force required to slide it also doubles. The ratio between the force required in sliding an object and the force pushing the surfaces against each other is its coefficient of friction. However, once motion begins the minimum force necessary to continue it may be contingent on the speed, typically diminishing with increasing speed. Engineers call this sliding friction to differentiate it from rolling friction, which we will discuss later.

    In certain instances, friction performs a vital role. For instance, it is necessary to the operation of belt drives, tires, parachutes, the synchromesh within a gearbox, drilling rigs, automobile brakes, and clutches. Additionally, a wheel requires friction to grip the ground or it would simply slide along as if it were on ice. Nevertheless, most of the time, it hampers the functioning of a machine and therefore engineers strive to reduce it to a minimum.

    A second constraining factor in machines is the elasticity of its parts. Bending because of transverse forces results in much greater deflection than plain tension or compression, and it increases with size. Although machine parts can be crushed under pressure, friction and elasticity are far more likely to interfere with its performance than the collapse of one of its parts.

    To review, a machine accelerates a small mass (effort) against resistance a large distance and simultaneously accelerates a large mass (load) a small distance; it is also reversible where a small load moves far or quickly and a large effort moves a small distance or slowly.

Simple Machines—The Inclined Plane


A simple machine is a device that makes work easier without consuming any energy except tiny amounts lost to friction i.e. their efficiency is very high; they are the building blocks from which all machines are made. Defined this way the inclined plane and the lever are simple machines; both make up the two bits of the binary language of machinery. Of the two, the inclined plane is paramount. All mechanical machines use the inclined plane principle, for it embodies the tenet upon which all machinery works: the trade-off between effort distance and load distance/velocity. In fact, we shall define any simple machine that does not have a fulcrum as essentially an inclined plane. The illustration provides an example. The pulley placed at D has a rope tied to load A and runs around to the effort at B.* Therefore, D to E serves as the effort distance and the incline C to D serves as the load distance, which in this case is twice the length of D to E leaving this inclined plane with an MA of two. Effort B only requires half the force because it must move twice the distance (D to E) to lift load A to exactly the vertical midpoint between D and E. Inclined planes can also be used in the reverse manner to speed things up i.e. an object moving from E to D can move faster than one moving from D to C but requires twice the effort exerted at A. Alternatively, an object moving from D to C can move faster that one moving from E to C. This has important implications for airfoils.

    Examples of inclined planes include just about everything from said airfoils to zippers, incisors to locks and keys, plows to spiral staircases, even to a rope pulling a sled/wagon! The classical inclined plane includes ramps, stairs, sloping ladders, slides, windshields, funnels, escalators, i.e. anything with a flat sloping surface. The wedge is merely a double inclined plane joined at the bottom that directs a force at ninety degrees perpendicular to the applied effort. It does this by concentrating an effort force at a broad end and directing it to a point, or much tinier area. Thumbtacks or nails demonstrate this: because the head is much larger than the point, the relatively small force exerted at the top is applied over a wide area and according to the work equation this gets concentrated to a much smaller area with much greater force. Examples include the cutting edges of knives, axes, chisels, razors, forks, hoes, and other such instruments. Pins, needles, ice picks, spears, nails, and other piercing devices are wedges as are jackhammers and tire treads. Additionally, we use wedges to hold things in place such as doorstops or conical valve heads. A screw is an inclined plane wrapped around a cylinder; it can change rotary motion into linear motion. Examples include wood screws, bolts, pipefittings, container caps/lids, pencil sharpeners, vices, worm gears, faucets, hose nozzles, and corkscrews. Some conveyor devices, such as an “Archimedean” screw, move material along between their threads as do drills, augers, mechanical moles, and meat grinders. The screw serves as the foundation for all propellers/fan blades in addition to screw jacks and some measuring instruments such as micrometers and calipers.

    A special device using the inclined plane principle includes a hydraulic machine. The illustration depicts two cylinders full of fluid with a pipe connecting them. If one applies a force (F1) downward on the left-hand piston, it generates pressure throughout the left-hand cylinder. This is analogous to an inclined plane’s effort distance. Let us say you apply a one newton downward force to the left-hand cylinder, and that the left-hand cylinder’s area is exactly one cm2. If the area of the right-hand cylinder is fifty cm2, and you push the left-hand piston down 50 cm, then the right-hand piston will rise one centimeter with a force of fifty newtons (F2). This is analogous to the load distance of an inclined plane. Of course, it also works in the reverse manner. Hydraulic cylinders of all sorts create mechanical advantage by using this simple force-multiplying effect. The principle at work here is that of the incompressibility of liquids where the pressure must remain constant throughout, aka Pascal’s principle. Engineers use hydraulic machines to drive everything ranging from garbage trucks to automobile power steering units. Other examples include the hydraulic press, the hydraulic jack, construction excavators, loaders, dumpers/tipper trucks, bulldozers, hydraulic cranes, pumps, automobile power brakes, hovercraft, carburetors/fuel injectors, syringes, aerosol liquids, fire extinguishers, scuba tanks, water meters, and the ink chamber of a pen.

* We shall see below how a fixed pulley offers no MA, only a change of direction.

The Lever


The lever is an adaptation of the inclined plane principle but because it is more sophisticated, it can accomplish more things. Levers come in three classes, but no matter what all levers consist of three components: a fulcrum or axis of rotation (the defining characteristic of all levers), an effort and effort arm, and a load and load arm. The longer the effort arm and the shorter the load arm the greater is the MA. The illustration provides a description of all three classes of lever.

    A first class lever places the fulcrum between the effort and the load, which changes the direction of force. Effort applied downward moves the load upward and vice versa. The most basic (and oldest) first class lever is the crowbar. Other examples of this type include the seesaw, hammer claw (to extract nails), fixed oars on a rowboat, and a balance beam scale. Two or more can be combined to form compound levers. Dr. James B. Calvert writes that “[h]and tools offer excellent examples: pliers, scissors, and similar tools are two levers joined at their common fulcrum, with the effort applied at one end by the closing of a hand.” (We discuss this more in the section on complex machines.)

    Probably humans then discovered pulleys, which are to quote Harry Walton “flexible levers.” Fixed pulleys are first class levers. The single fixed pulley is a wheel that has a groove around the outside edge, which a rope, chain, or belt moves around. Pulling down on the rope lifts an object attached to the other end. Work becomes easier because pulling down is aided due to the assistance of gravity. A single fixed pulley offers no force/distance trade-off it only provides a directional change i.e. there is no MA. A single fixed pulley can be fastened around a second fixed pulley, but if both are of identical size the only benefit is the choice of which direction the pulleys will turn i.e. clockwise or counterclockwise. If we crisscross the rope or belt that links the two, it switches the direction in which the driven pulley turns. However, if the fixed pulleys differ in size then we gain a definite MA as the first pulley, attached to an energy source, transmits a continuous torque (rotational force) to the second. Examples of fixed pulleys include flagpoles, clotheslines, window blinds, drapery pulleys, bucket hoists in wells, sail hoists, ski lifts, and automobile engine belts.

    The wheel and axle is by far the most important form of first class lever. It is a rotary lever where the effort and load move a full 360 degrees; below is an illustration. A wheel and axle has a larger wheel (or wheels) connected to a smaller cylinder (axle) so that they form concentric circles and turn together. When the wheel is turned, it moves a greater distance than the axle, but requires less force to move it. The axle moves a shorter distance, but it takes greater force to move it. Therefore, like all machines, it can reduce a force that is necessary to accomplish a task only by increasing the distance that the force acts over; of course, it works in the opposite fashion. 

    Additionally, the wheel and axle provides tremendous advantages vis-à-vis the field of transportation. Prior to the invention of the wheel travois and sledges provided a means of moving goods and people. However, friction hampered the effort. With the invention of the wheel, this problem was greatly reduced. Rolling friction is significantly lower than sliding friction, and virtually disappears, when the surfaces making contact are rigid and smooth and no deflection occurs. For example, imagine a wheel riding on any hard surface. If both are perfectly hard and the road flat, the effort to start motion is zero for an infinite load that we place over the axle. (The same applies to the placement of a load in the hull of a ship). The load is immobile and can’t move downwards, so the VR is zero; therefore the MA becomes infinite, the product of these equaling one. However, friction is constantly ever-present, and we must apply some effort in surmounting this force. Additionally, the road itself needs to be inclined. “Dragging a load using a wheeled cart,” writes Chris Woodford,  


is far easier than dragging it on the ground—for two reasons: [w]heels reduce friction. Instead of simply sliding over the ground, the wheels dig in and rotate, turning around . . . axles. That means the only friction [that has] to [be] overcome is at the point where the wheel and axle meet—between the relatively smooth inner surface of the wheels and the equally smooth outer surface of the axles around which they turn.

    Wheels [also] provide leverage (in other words, they are examples of force multipliers or simple machines). A cart with bigger wheels is easier to push because its greater-diameter wheels work like bigger levers, multiplying the pulling or pushing force and making it easier to turn the wheels around their axles—in exactly the same way that a long spanner makes it easier to loosen a nut.

    . . . By helping us to move loads, harness energy, and transform forces, this simple but amazingly effective invention literally made it possible for people to conquer the world!


The ball or roller bearing is another example of rolling friction reduction where the “road” turns up into a loop that is continuously travelled; one place they find a use is between the wheel and its axle.

    Examples of the wheel and axle are ubiquitous. To begin with, let’s first cite the potter’s wheel, one of the most ancient representative of the class. But the wheel and axle has far surpassed this function; it also include doorknobs, steering wheels, turbines, waterwheels, windmills, Ferris wheels, screwdrivers, stopcock valves, winches, capstans, windlasses, and all types of transportation wheels whether attached to wagons, skates, bicycles, hand trucks, wheelbarrows, or motor vehicles.    

    Simply by adding teeth around the rim of a wheel humans invented the gear, which is able to alter the torque of a machine or the distance/velocity it moves. Gears always operate in pairs to transmit motion; this is accomplished by having two-toothed wheels fit together either directly or through a chain or belt so that one wheel will turn the other. Some gears may incorporate a screw in the form of a worm gear or a toothed shaft in place of one of the wheels. Gears of differing size provide an MA. A gear may also be a combination of toothed wheels that produces a certain speed (such as a bicycle’s top gear that makes the bike go fast, or the low gear for slow speed), or gears may simply change the direction of motion. Many types of gear abound including the spur, helical, bevel, worm, planetary, and rack and pinion. Examples of machines using them include mechanical clocks, motor vehicles, drills, manual can openers, and bicycles, which provide an excellent example: by using different gears, the cyclist can alter how fast he or she travels on flat terrain or their ability to climb a hill slowly—all without altering their rate of peddling. Another usage for gears came about in 1781 when James Watt found a special application for them when he was unable to obtain a crank for his steam engine (the crank was under patent at the time). His sun and planet gear did the same thing as a crank—it converted the reciprocating motion of his piston-beam into rotational motion. Doubtless, he would have preferred to use a crank.

    Cranks and cams are another variety of the wheel and axle. A crank has a rod attached to an axle or shaft. This rod has a perpendicular bend that proceeds for some length before bending again to be parallel with the first rod; this forms the wheel component. Engineers use it to change reciprocal motion into rotary motion or vice versa. The muscle of an automobile engine is its crank; it has a piston and connecting rod joined to it with a plain lever linkage and it spins a flywheel. The cam does the opposite; it works to turn rotary motion into reciprocal motion. The heart of a cam is a rotating egg-shaped component, the cam, in contact with a follower. It is helpful if we want a variable velocity ratio, or the basic motion of one part of the machine needs modification into a more complex motion somewhere else. As an example, cams activate the valves that open and close in an automobile’s cylinders. They also work in an electric toothbrush when they cause the brush head to move back and forth when connected to an electric motor. The eccentric crank, applied where a crank along the shaft is not suitable, or where the crank angle necessitates that it be changeable, is a type of cam. An example is the steam engine, which uses them to change rotary into reciprocating motion to push a sliding valve.   

    A second class lever places the fulcrum at one end. To gain an MA we place the load closer to the fulcrum than we place the effort; in this fashion, the second class lever reduces the effort necessary to move the load because it moves a greater distance. With this kind of lever, the direction of effort is not changed. Pulling up on the second class lever arm pulls up on the load and vice versa.  

    The movable pulley helpfully demonstrates this principle. In the illustration, the fulcrum is attached at the top and each strand carries only half the load but the effort must move twice the distance. In multiple movable pulleys, a succession of pulleys linked with a single rope substitutes lever arms with wheels. Tugging on the loose end of the rope is tantamount to working the effort arm of a lever, and counting the number of strands going to and coming from the moving pulley that supports the load provides the MA gained i.e. every time the rope wraps around a wheel it generates a greater MA. Examples of second class levers include wheelbarrows, doors or gates, wrenches, hinged lids, pedals, paper cutters, hole punches, nutcrackers, garlic presses, bellows, canoe paddles, bottle openers, even two people who carry a pole between them that has a load attached in between. Multiple movable pulleys require the assistance of fixed pulleys to function. Examples here include escalator and elevator pulleys, construction cranes, differential hoists, and the block and tackle.

    A third class lever has the effort lying between the load and the fulcrum, which is still placed at one end. With this configuration the direction of effort is not changed (the load moves in the same direction as the effort as in a second class lever), but the gain offered is an increase in the distance (velocity) the load moves. In contrast to other machines, this type of lever requires an increase in the applied input force, but allows a greater degree of control over the output force. An example of a third class lever includes the club/bat. The fulcrum is at the base (usually the person’s wrist), the effort applies above it, and the load is at its end. Other examples include a hammer, fishing pole, sling, hockey stick, tennis racket, catapult, shovel, pitchfork, hoe, rake, scythe, broom, kayak paddle, tongs, handle (e.g. axe, knife, or brush), tweezers, pens, staple removers, the mandible, and arms and legs.



There are clever devices that, though not by definition machines (because they do not change their input force and convert it into an output force), are extremely significant parts of machines. Engineers call them mechanisms and they facilitate the transfer of a force by forming the intricate interconnections within a machine.

    Examples include springs, clutches, bearings, couplings/linkages, weights, and flexible objects like ropes, belts, cables, or chains. Springs, which engineers call accumulators,* change their shape in response to an external force and return to their original shape when the force ceases. Generally, the amount of the shape change directly relates to the amount of force exerted. If too large a force applies, however, the spring will permanently deform and never return to its original shape. Pneumatic powered machines act as springs: the energy used to compress the gas later releases to do useful work in moving a load. This type of device does not burn the gas it just releases it. Examples include jackhammers, riveters, rock drills, paint sprayers, vacuum machines, even blowguns. A linkage, a common mechanism, transfers a force along an axis. A slotted link with a sliding block can allow a fluctuating amount of motion to be transferred.

* This term refers to an energy storage system; essentially any system that can store and release thermal, electrical, or mechanical energy is an accumulator.

Complex machines


Complex machines are nothing more than a combination of simple machines and mechanisms; we’ve already seen how levers can be joined together to act as one complex machine. Engineers have found ways to combine simple machines in an unlimited manner to perform any task. One example is the clock. Calvert writes that


    The clock is a fascinating sort of machine, full of simple machines. . . . The input is the effort exerted by a weight or spring, and the output is simply movement proportional to time, or the triggering of subsidiary actions such as ringing bells. The essential part, the escapement, involves inertial forces, but simple machines can be identified in it. The earliest mechanical escapement was the foliot and verge escapement. . . . The crown wheel is part of a wheel and axle, driven by a falling weight. The foliot, or “balance,” is not actually a balance. It supports two weights at a distance from the axis formed by the verge. These weights are driven back and forth through a limited arc by pressure against the pallets on the verge. The pallets are cammed by the steep edge of a tooth, at first forcing the wheel backwards slightly as the weights are brought to a rest, recovering their energy, then forwards as the weights are accelerated. The recoil of the crown wheel is a feature of all early escapements. When a pallet moves free, the opposite pallet then comes into play as the wheel snaps forward a little. This pallet then decelerates the weights, and the cycle continues. Its very great mechanical advantage is the positive nature of its motion, very useful with friction and rude construction. A train of gears driven by the crown wheel, with final ratios of 1:12:60, drives hour, minute and second hands. Moving the weights out or in regulates the clock. The application of the pendulum, which has a natural frequency, to control the escapement led to much more accurate clocks. At first, the pendulum worked a verge, but the anchor escapement allowed a much smaller pendulum swing, which meant greater accuracy.


    Another complex machine is the engine. Engine and machine are actually two words for the same thing derived from Latin and Greek respectively. An engine aka a prime mover is a machine that uses energy as provided by nature (e.g. fuel or wind) and transforms it into mechanical energy (i.e. force and motion). Examples of prime movers include animal muscle, airfoils in the form of sails, waterwheels, windmills, and turbines (engines that obtain energy from the motion of a liquid or gas). The electric generator, which transforms the energy of falling water or of steam into electrical energy, is an example of a turbine. Alternatively, the input itself could be electrical; the electric motor transforms electrical energy into mechanical work. But of all engines the most important is the heat engine (i.e. the steam engine/turbine or the internal-combustion engine) which converts a chemical fuel into mechanical energy. They are ubiquitous in the modern world.

    Engines existed for millennia before a scientific basis for them was developed. This came about in 1824 when Nicolas Léonard Sadi* Carnot published his Reflections on the Motive Power of Fire. Carnot concluded that to increase the efficiency of any heat engine it must function between the greatest possible temperature differences. Since his time, engineering has been a continuing attempt to build engines that did just this.  

* Ed. Note: Carnot’s father gave him this name to honor the Persian poet from Shiraz. 

Self-controlled machines and electronics


Control systems often include machines that regulate processes; examples include the production of gasoline within an oil refinery, or the manipulation of flight surfaces of an airplane. There are two basic types of control system: feedforward and feedback. An example of feedforward would be a machine used to copy keys, where a master is copied on a lathe and tracing forward the design produces a duplicate. Feedback systems use information from a process to correct the machine’s operation, for instance that of a home thermostat.

    An electronic machine uses electricity to control electricity. Our authors David Macaulay and Neil Ardley write that


Electrons can be forced into a wire in varying quantities, and they give rise to varying levels of electric charge that travel almost instantly along the wire. . . . This varying charge constitutes an electric signal, and it can govern the way in which a machine works . . . the signal may simply switch the machine on or off, or it may control signals that enable the machines to control themselves. . . .


The computer uses the former method—where a signal simply turns on or off a myriad of electronic switches that enables it to function. Essentially, a computer is a huge electronic switching device, and the modern world could not do without them!

    First, we need a little primer. A fundamental physics principle known as Ohm’s law is the basis of all electronics.* Whatever jobs an electronic component performs it does so by controlling the flow of electrons through its structure in a very precise way whilst observing Ohm’s law. The majority of these devices are composed of solid bits of partially conducting, partially insulating substances referred to as semiconductors. Adding select impurities (doping) to a semiconducting crystal alters the electrical properties of the semiconductor and improves its conductivity. Because electronics involves understanding the precise mechanisms of how solids let electrons pass through them, scientists and engineers refer to it as solid-state physics. An electric current is the flow or movement of charged particles. The energy of a current (amperage) fluctuates depending on the variations of charge along the conductor. Engineers call this the potential difference and they measure it in volts. The nature of the conductor greatly affects voltage. Certain materials conduct electricity much more easily than do others. Electricity is frequently compared to a waterfall. The amperage represents the amount of water, the voltage represents the altitude of the waterfall (the greater it is the more potential energy the water would have due to its height from the top and the greater energy it will have when it strikes the bottom), and the resistance is analogous to rocks in the current that constrict or even stop the flow of water; engineers measure it in ohms. Lastly, an electric current either flows in the same direction (DC) or flows back and forth around a circuit many times a second (AC). Electricity is all about making electromagnetic energy flow around a circuit (whether AC or DC) so that it will drive something powerful like an electric motor, a heating element, or appliance. Generally, all these need a great deal of energy to make them work so they use quite large electric currents. Electronics on the other hand involves tiny amounts of electricity that are modified in some way to carry a signal, i.e. a variation in an electric voltage or current used to carry information. Chris Woodford makes the analogy that we should think of something like a microwave oven to easily see the difference between ordinary electricity and electronics. In a microwave, electricity provides the power that generates high-energy waves that heats the food; electronics controls the electrical circuit that carries information on what needs to be done to cook the food. Small electric currents are precisely controlled to flow around much more complex circuits in order to process signals (such as those that carry radio and television programs) or store and process information. Finally, there are two basic types of electronic signals: analog and digital. In an analog signal, certain constantly varying aspects of the electrical current represents the information. In contrast, digital signals use standardized pulses to represent numbers.   

    The key to an electronic device is the way engineers arrange components in circuits. Normally the more complicated the circuit, the more sophisticated the operations it can accomplish. As Chris Woodford points out the simplest possible circuit is a continuous loop connecting two components like two beads fastened on the same necklace. Analog electronic devices usually have much simpler circuits than do digital ones. A rudimentary transistor radio may have a few dozen distinct parts and a circuit board probably no bigger than the cover of a paperback book. However, in something like a computer, which uses digital signals, circuits are much more complex and can have hundreds to millions of distinct pathways.

    The elements of a circuit include passive components and active components; passive components either transform electric energy into heat or store it internally. They include resistors, capacitors, inductors, and transformers. Resistors apply additional resistance to the system, reducing the current (or increasing the voltage) over a segment of wire producing heat and, in turn, dissipating power. A resistor plays an important role in a system because it can keep it from overloading or overheating a piece of electronic equipment. A capacitor holds onto a small amount of charge, like a very tiny battery. As charge builds up in the capacitor it repels further charge, slowing the flow of electricity, blocking a direct current but allowing an alternating one to pass. An inductor is a coil of wire that, as current flows along it, builds up a magnetic force that causes the electricity to flow more slowly through it. An inductor impedes the flow of alternating current but allows direct current to flow. Engineers define a transformer as two inductors sharing the same iron core that either increases or decreases the voltage of alternating current by increasing or decreasing the amperage via electromagnetic induction. We find all these components in electrical devices as well as electronic ones.

    Active components either modify a signal, direct it to a particular location, or amplify it,* and we find them only in electronic circuits. They include transducers, switches, diodes, optoelectronic devices, amplifiers, and transistors; engineers use all to control the flow of electric current in a circuit to process a signal. Transducers convert one form of energy into another. Various transducers convert mechanical vibrations into electric waves—or vice versa. Switches turn the flow of current to a circuit on or off. Diodes allow an electric current to flow through them in only one direction and are known as rectifiers. Engineers use diodes to change AC into DC. They can turn electromagnetic waves that travel as AC into DC. Optoelectronic components are various devices that can turn light into electricity or vice versa. An amplifier strengthens a weak fluctuating signal (i.e. it transforms tiny electric currents into much larger ones). The triode, a direct descendant of Edison’s light bulb, gives us an early example of an amplifier. A triode, as its name suggests, is composed of three electrodes: a cathode producing electrons, an anode receiving electrons, and a grid in between them that carries the varying voltage to be amplified. When electrons leave the cathode in a triode the grid allows the electron current to vary, which then flows through a resistor. This converts it into a magnified copy of the input voltage. An amplifier can also be turned into an oscillator that produces continually repeated patterns of voltage or current. Oscillators provide power, movement, or timing for machines. They can turn DC into AC, move an electron beam, supply timed pulses to control a computer, or generate waves that carry signals though cables or space. Transistors, invented in 1947, are able to switch minute electric currents on and off or to amplify them. Those that function as switches operate as components in the memories of computers, while those operating as amplifiers strengthen weak electrical signals into stronger ones and thereby allow a small amount of power, representing information, to control a much larger amount of power that can do useful work as in powering a loudspeaker, monitor, or computer display. When transistors connect together, they make devices called logic gates that can carry out very basic, elementary manipulations on bits (0s and 1s). Utilizing Boolean logic, and when combined in certain combinations, these simple circuits can perform any logical or arithmetic operation that can be defined in a finite number of steps.

    In the late 1950s engineer Jack Kilby and physicist Robert Noyce independently developed a way of creating transistors and electronic components in miniature form on the surface of a piece of silicon. It quickly became feasible to jam hundreds, thousands, millions, and then billions of miniaturized components onto chips of silicon about the size of a fingernail. The use of this integrated circuit (IC) led to the development of more advanced computers.

    The development of the microprocessor in 1971 from the IC led to a burgeoning of technology. Home computing became a reality, for a microprocessor contains the entire central processing unit of a computer on a single IC. It can interpret and execute program instructions as well as handle arithmetic operations, and store the results temporarily. Microprocessors find a place in virtually every consumer device that uses electric power; examples include automobile engines, gasoline pump dispensers, microwave ovens, video recorders, cell phones, digital cameras, and hand-held computers. High-performance microprocessors function in the servers that store and distribute Web content, as the high-speed network switches that function as the Web’s infrastructure, in the streaming of audio and video content, and in desktop computers. Lower-powered microprocessors find a use as the core of notebook computers and electronic games. They also furnish the control and flow logic of hand-held devices, cellular and cordless phones, digital cameras, and the diagnostic and pollution control systems of automobile engines.

    Engineers have installed microprocessors in the hardware of robots and it is in this application that the future of the microprocessor lies. Mounted directly in a robot it can instruct it to carry out operations stored in the computer’s memory. Consequently, microprocessor-controlled robotic devices have already revolutionized assembly line techniques and in the future promises much more advances in technology. But alas will robotic man, Homo roboticus, ever acknowledge his humble beginnings?

* Ohm’s law, named for German physicist Georg Ohm, states that a circuit contains a voltage directly proportional to the current multiplied by the resistance encountered by the current in that circuit. Mathematically this is V = IR.

* This is the very definition of a machine!