170 RESISTANCE AND PRESSURE OF FLUIDS. 



EXAMPLE. 



What is the discharge under a head of water of 3 feet 

 through a tube 2 inches in diameter, whose coefficient of 

 resistance is ft = 0.4 ? Here from (10) we have 



= ~ = 0.845 ; 

 VI. 4 



hence, from (1) of Art* 93, we have, for the actual veloc- 

 ity *>i, 



= 0.845\/64.4x3 

 = 0.845x8. 025 A/3 = 11.745 feet; 

 k = (-fa) 2 * = 0.02182 square feet; 



hence, the required discharge, from (1) of Art. 94 (since 

 a = 1) is 



Q = kQ'JZgh 



- 0.02182 x 11.745 = 0.256 cubic feet. 



97. Resistance and Pressure of Fluids. (1) By 



the resistance of fluids is meant that force by which the 

 motions of bodies therein are impeded. The resistance of a 

 fluid to the motion of a body is. occasioned by the force 

 necessary to displace that fluid. Since the motion commu- 

 nicated to a body at rest by another body impinging on it 

 with a certain velocity is equal to the motion lost by the 

 impinging body, therefore the motion communicated to the 

 displaced fluid must be the same as that of the moving 

 body ; hence the work which the fluid destroys in the mov- 

 ing body will be equal to the work stored in the fluid. 



Let a = the area of the front of the body presented to 

 the fluid, v = the velocity of the body, w = the weight of 



