FLOW OF WATER THROUGH PIPES. 



127 



16.1 feet during the first second, and at the end of 

 that time has acquired a velocity of 32.2 feet. The 

 velocity at the end of each succeeding second of time is 



32.2 feet greater than it was at the end of the precede 

 ing second. This is called the accelerating force of 

 gravity and is usually designated by £•. Knowing 

 the height that the body has fallen at any time, the 

 velocity may be determined. The following table 

 shows at once the relation of time, space, velocity, and 

 accelerating force of the action of gravity upon falling 

 bodies during the first five seconds : 



FALLING BODIES DURING FIRST FIVE SECONDS 



t 



Time. . . 



I sec. 



2 sec 



3 sec. 



4 sec. 



S sec. 



Space ~ h 



Velocity = v.. 

 Accel, force = g. ... 



16.1 

 32 2 

 32.2 



64 4 

 64 4 

 32.2 



144 9 

 96 6 

 32.2 



257 6 



128 8 



32.2 



402. s 



161 .0 



32.2 



Water flowing down an inclined surface would follow 

 the same law were it not for resistances of various 

 kinds which constantly act upon the particles of water 

 as they descend and produce a uniform flow where the 

 resistance is constant. Were this not the case, our 

 ponds and lakes would soon become dry, and our 

 brooks and rivers would for a time become dangerous 

 torrents- The equilibrium of natural forces would at 

 once become unbalanced. 



It has been the life-long work of many eminent hy- 

 draulicians to determine by practical experiments the 

 value of these retarding forces and by introducing them 

 into the gravity formula to so modify it that it shall 

 be a correct expression for the flow of water under given 

 conditions and thus become of use in practical affairs. 



