202 



SUDDEN CONTRACTION OF SECTION. 



somewhat modified by friction. For water entering a cylin- 

 drical pipe from a reservoir of indefinitely large size, experi- 

 ment shows that ft is increased by the resistance at the 

 entrance into the pipe, and by the friction of the water in 

 the pipe, to 0.505, so that (1) becomes 



Aj = 0.505^- (3) 



9 



(2) If there is a diaphragm at the 

 mouth of the pipe, as at AB, Fig. 57, 

 with an opening ab, whose cross-section 

 is smaller than the cross-section of the 

 pipe CEDF, let a' be the area of this ori- Fi 9- 57 



fice. Then if c is the coefficient of con- 

 traction as before, the area of the contracted stream is ca', 

 and the velocity v' at the contracted section will be 



v -, v, 

 ca 



hence, the head lost in passing from the contracted section 

 to the pipe at EF is 



) 2 _ ( a 

 ~ = \ca' ~ 



where the corresponding coefficient of resistance is 



(5) 



SCH. 2. Weisbach has found experimentally the follow- 

 ing values of the coefficients c and j3, when the stream ap- 

 proaching the orifice, as in Fig. 57, was considerably larger 

 than the orifice.* 



* Ency. Brit., Vol. XIII., Art. Hydromechanics. 



