ENERGY 



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ENERGY 



ENERGY, en'erji, the name given in physics 

 to the capacity possessed by matter for doing 

 work. Energy is one of the two fundamental 

 ideas of physics, the other being matter itself. 

 Motion, heat, light, sound and electricity are all 

 energy expressed in different forms. See PHYS- 

 ICS. 



The great source of energy is the sun, and 

 this solar energy has been accumulating since 

 the beginning of time. On earth the energy 

 originally derived from the sun which man is 

 able to apply to his own purpose is stored up 

 in coal, wood and oil; in food; in the tides 

 and waterfalls and running streams; in the 

 wind; in the muscular energy of the animal 

 world, and in hundreds of other familiar forms. 

 The process of transferring energy from one 

 body to another is called work, and we meas- 

 ure work and energy by the same units. 



Types of Potential Energy. The two great 

 divisions under which all energy is classified 

 are potential and kinetic, and whatever is not 

 one is the other. Energy which is slumbering 

 or lying hidden is known as potential energy, 

 or energy of position. Work has been done 

 upon certain matter that is, energy has been 

 expended upon it giving it in turn a power to 

 work which is only awaiting the proper touch 

 to become active. A locomotive under a full 

 head of steam, waiting for the exact moment 

 of departure; a boat held down by its anchor, 

 its sails bulging with wind; a racehorse listen- 

 ing for the starting gun; a baseball in the 

 pitcher's hand; a loaded gun; a boulder bal- 

 anced on a hillside; a tightly-coiled spring; a 

 hammer poised in air; a bent bow, ready to 

 let fly its arrow, or a stretched elastic band of 

 any kind; an uulighted match; a charged bat- 

 tery; a tank of gasoline, or a lump of coal 

 all these are examples of potential energy. 



Types of Kinetic Energy. Kinetic comes 

 from the Greek word meaning move, and 

 kinetic energy is therefore the energy of mo- 

 tion, or energy which is in actual operation. 

 The moving train; the boat in full sail; the 

 horse speeding toward the tape; the ball or 

 bullet flying through the air; the boulder 

 rolling down to the foot of the hill; the un- 

 coiling spring; the hammer striking the anvil, 

 or the weight falling to earth; the bow or the 

 elastic snapping back to its original shape; the 

 burning match; the battery releasing its elec- 

 trical charge in the form of a current; the 

 gasoline or coal in combustion, giving life and 

 power to the engine these are all everyday 

 illustrations of what we call kinetic energy. 



The Constant Transformation of Energy. 

 Every change that takes place in the universe" 

 results from the change of kinetic energy into 

 potential, or potential into kinetic a process 

 called the transformation of energy. When a 

 boy, for instance, puts a stone in the pocket 

 of a slingshot and stretches the rubber, the 

 stretching process develops kinetic energy 

 transferred from the potential energy in the 

 boy. This kinetic energy, in turn, becomes 

 potential energy in the rubber band, so long 

 as he holds it stretched. When he releases the 

 band the potential energy is transformed into 

 kinetic and is transmitted to the stone. When 

 the stone hits, the energy is transferred to the 

 object struck, once more becomes potential 

 energy, and would reveal itself to our touch 

 in the form of heat. 



The Great Law of the Conservation of En- 

 ergy. By the phrase conservation of energy is 

 meant that the amount of energy in the uni- 

 verse is always the same, that it can neither 

 be increased nor diminished. It can be di- 

 rected, but it cannot be created or destroyed. 

 It is conserved kept. Thus, if energy disap- 

 pears in one form, another form replaces it 

 in precisely, the same amount. 



The pendulum is an example of the way in 

 which energy changes and is conserved. When 

 we draw the bob aside from a to b, as shown 

 in the illustration, we are doing work upon it, 

 for we are lifting it in space the distance ad. 

 Thus we have 

 stored up poten- 

 tial energy, which 

 begins to change 

 into kinetic the 

 moment we let it 

 drop, is wholly 

 kinetic at a, and 

 again wholly po- 

 tential at c, but 

 with the total 

 energy always the 

 same. The pen- 

 dulum has raised MOVEMENT OF THE 

 itself through an PENDULUM 



arc (ac) equal in Illustrating the transfer- 

 length to the arc mation of energy ' 

 through which it was lifted (ab) ; that is, it has 

 put forth as much energy as was put into it 

 no more, no less. The pendulum would continue 

 to swing back and forth forever, exchanging 

 potential energy for kinetic, and vice versa, 

 if it were not for friction and the resistance 

 of the air. However, the energy used up in 



