CHAPTER XV 



SOME SIMPLE MACHINES 



Give me a fulcrum on which to rest and I will move the earth. ARCHI- 

 MEDES. 



This has been aptly called an age of machinery. The food 

 we eat, the clothing we wear, the houses we live in, the furniture 

 that contributes to our comfort, are all largely prepared for us 

 by machinery. We ride to school or to work in a machine, 

 we travel by machinery, our work is largely done by the machines 

 we direct. We farm by machinery, and machines mine our 

 coal, furnish our light, load our ships, sweep the floor, wash the 

 clothes, pump the water. They are our omnipresent servants; 

 at every turn we see them at work. Yet they are all applications 

 and combinations of three simple types of machines the lever, 

 the pulley, and the inclined plane that have been in use ever 

 since the earliest glimmerings of civilization. We think of the 

 invention of the steam engine as a revolutionary event. Yet the 

 savage who first discovered the use of the lever made even a greater 

 contribution to man's advancement. It will be worth while to 

 understand the principle of operation of these simple machines 

 and see some of their commonplace applications. 



There are one thousand and one applications of the lever 

 about us in the home, in industrial life, and in our own bodies. 

 Nearly every child has had experience with the teeter. A board 

 is put over a log or saw horse, so it about balances at the middle 

 point; then a child sits astride on either end, and they go up and 

 down alternately as first one, then the other, gives a little shove 

 as his feet strike the ground. This is a simple lever with its 

 arms of equal length, and the point on which it rests, the fulcrum, 

 at its center. If, now, one child is considerably heavier than 

 the other, the board must be moved along on its support so that 



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