MECHANICS OF LIQUIDS 73 



can deliver in the course of 10 to 15 minutes is utilized in 

 the hydraulic machine within a few seconds. This is not 

 possible in the use of any other form of machine tool. 



72. Capacity of Pipes. In computing the capacity of 

 pipes used to convey liquids one should remember that the 

 capacity varies with the area, and that the areas of similar 

 figures vary as the squares of their corresponding dimensions. 

 Pipes being cylindrical in shape are, therefore, similar figures. 

 The areas of any two pipes are to each other as the squares 

 of their diameters. 



Thus, if one pipe is in. in diameter, and another is 3 in. in di- 



Q f\ 



ameter, their ratio is , or 4 to 1, and the area of the larger one is, 



y 



therefore, 4 times that of the smaller one. 



73. Water. A manufacturer usually stores quantities of 

 water for manufacturing purposes in a tank at the top of 

 each of the different buildings of the plant, but in case the 

 factory or mill is near a stream, the water is stored in a dam, 

 at a convenient height. The pressure of the water against 

 the sides of the tank or dam is exerted perpendicularly to 

 the surface on which it bears. Every pound of water in a 

 tank or dam at some height above the point where the 

 water is to be used possesses a certain amount of potential 

 energy due to its position. To illustrate: W Ibs. of water 

 raised a definite height H possess the capacity of doing work 

 which is equal to the weight of water in pounds multiplied 

 by the height in feet. The result is W X H ft.-lbs. 



To estimate the energy in the reservoir of a city or town 

 so as to know the exact water pressure, it is necessary to 

 know the perpendicular height from the water level in the 



