THE MECHANICAL POWERS. 



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EXAMPLE. What is the length of the inclined plane of a 

 screw of 12 inches circumference and 1 inch pitch ? 



SOLUTION. 12 2 + 1 2 =145 and ^ 145 =12.04159 inches. 

 Ans. 



N OTE> It will be observed that the length of the plane as 

 given in the above example is the length of only one turning 

 of the screw, or the length of once round the circumference, 

 which, in ascertaining the power of a screw, is all that is 

 necessary to be known of the length. The entire length of 

 the plane and the entire height of the screw have nothing 

 to do with its power. A single section, comprising one 

 revolution of the plane or the cylinder, is enough. 



To find the power required to raise a given weight by 

 means of a screw of given dimensions. 



KULE. As the length of the inclined plane is to the 

 pitch, or height of it. so is the weight to the power. 



EXAMPLE. What is the power requisite to raise 9000 Ibs. 

 by a screw 15 inches circumference, and 1 J inches pitch ? 



SOLUTION. 15' + 1 2 =227 and 4/227^=15.62 inches, 

 length, then 15.62 inches, length, : 1J- inches, pitch, : : 9000 

 Ibs., weight, : 864.27 Ibs. Ans. 



NOTE. When a wheel or capstan is applied to turn the 

 screw, the length of the lever is the radius of the circle 

 described by the handle of the wheel or capstan bar, and 

 half the diameter of the screw is the radius of the axle. 



When the screw is turned by a wheel, a crank, or capstan, 



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