CHAPTER XXVII 

 MACHINES 



153. Mechanical Advantage. A machine is a contrivance 

 for transferring or transforming energy, and therefore can 

 never give out more energy than is put into it. A " perpetual 

 motion" machine is mechanically impossible. One of the 

 advantages of a machine is that it can turn a small force applied 

 for a long time at one point into a larger force for a short 

 time at some other point, and thus a feeble force may be made 

 to accomplish great things. By means of a strong bar, we 

 may raise a stone that we could not move otherwise. It 

 will be noted, however, that the stone moves only a few inches 

 while the end of the bar to which the pressure is applied is 

 moving much farther. That is, a small force acting through a 

 foot or more has been transformed into a greater force acting 

 through a few inches. The force applied to the machine is 

 called the effort, or power, and the force the machine exerts is 

 the resistance or weight overcome. The ratio of the resistance 

 to the effort gives the mechanical advantage of the machine. 



154. Simple Machines. There are but six types of simple 

 machines in the world. All more complex machines, whether 

 watches, dynamos, steam engines, automobiles, or printing 

 presses, are merely combinations of these simple machines 

 which are so familiar to us that we scarcely think of them as 

 machines at all. These simple machines are the lever, the 

 pulley, the wheel and axle, the inclined plane, the wedge, and 

 the screw. As a matter of fact, the principles upon which 

 they operate may be further reduced to two the lever and 

 the inclined plane. 



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