308 FORMS OF ENERGY screw or jack is an example of a special type of inclined plane; thus a screw is forced into wood slowly with little power, while a nail is forced into it quickly with more power. A jack may be used to raise a heavy automobile because it enables a man to do a given piece of work by exerting his A wedge is limited effort over a shorter distance in a given time. a double inclined plane that enables man to increase his force by decreasing the distance through which a force acts in a given time. "Give me a place to stand and rest my lever on and I can move the This great mathematician and inventor was man to set forth the principle of levers, which he applied in earth," said Archimedes. the first constructing machines of warfare. (A Bent Lever) Claw Hammer Paper Shears f^u- R. - - ^^,j^^gj Barrow Fig. 103. To which class does each of these ever>'day levers belong? (From Pieper and Beauchamp's Everyday Problems in Science, published by Scott, Foresman and Company.) Every lever must have a bar and a pivot called the fulcrum. Some common examples of levers are typewriter keys, automobile brake pedals and clutches, piano keys, scissors, teeter-totters, arms, and legs. Levers are classified as to the relative positions of the fulcrum, the effort (force), and the resistances, as shown in Fig. 103. The lever aids man in doing work, for it enables him to exert a great force to move an object a short distance by doing an equal amount of work in which his limited force is made to act through a long distance. In addition to these three simple levers there are circular levers — wheels, axles, and pulleys. The ordinary cart wheel is merely a device to lessen friction and is not classed as a machine. The wheel and axle, and pulley, on the other hand, are used to transmit and modify force and motion. Thus the motion of a slowly moving large wheel of a powerful engine may be distributed by belts, pulleys, wheels, cranks, and gears to a large number of rapidly moving parts. All of the marvelous machines of today are examples of various combinations of these six simple machines — the lever, the wheel and
MACHINES HAVE RAISED LIVING-STANDARDS 309 axle, the pulley, the inclined plane, the screw, and the wedge. These machines, in turn, are simply devices to give the advantage of increased speed, distance, or force. The Invention of the Steam Engine Brought About the Industrial Revolution. The invention of the steam engine, like many other important inventions, represented the bringing together of a number of different observations and simple devices; no one can be given credit for discovering the principle of the steam engine. Hero (between 100 B.C. and 200 a.d.) is credited with inventing the earliest steam engine, in which the recoil of steam issuing from a jet was used to make an arm carrying the jet move about an axis. Up to the eighteenth century the chief hindrance to industrial development was the lack of power. Men, women, and children did back-breaking work from twelve to eighteen hours per day, animals were likewise overworked, and yet the results were comparable to what one would accomplish by attempting to cut a square mile of wheat with a hand sickle. Many mines used as many as five hundred horses to get the water out of the workings and were often abandoned after losing the battle with subterranean water. It is true that windmills and water wheels had been put to work in the service of man, but no way had been discovered to transport the energy thus made available to industrial centers. Guericke had demonstrated in the seventeenth century that a piston would be forced into a cylinder by the pressure of the atmosphere when a partial vacuum was produced between the piston and the bottom of the cylinder. The Dutch physicist, Huygens, tried exploding gunpowder in the bottom of the cylinder to force the air out through a valve in the piston, but this explosion engine was not efficient, and it was dangerous to use. Denis Papin, who was engaged by Huygens to work on this explosion engine, proposed to produce the vacuum by the condensation of steam. Papin heated water in the cylinder to generate steam and then cooled the cylinder to condense the steam. Obviously, this alternate heating and cooling process was not very practical. In 1712, the year in which Papin died, Thomas Newcomen invented a steam engine in which he separated the steam boiler and the piston. The machine made four strokes a minute, but the addition of a jet of water inside of the cylinder to cool it increased the speed to twelve strokes a minute. James Watt, a mechanic at the University of Glasgow, was one day given the job of putting in order a small model of a Newcomen engine.