224 UNIFORM MOTION. 



From (2), we have the width at the bottom, 



25 



x = -- - 3.609 cotan 40 

 o. buy 



= 6.927 4.301 = 2.626 feet. 

 The width of the top, from (6), is 



CD = 2.626 + 7.218 cot 40 = 11.228 feet 

 The wetted perimeter is 



sn 



7218 



= 2.626 + . , = 13.855 feet ; 

 sin 40 



and the ratio which determines the resistance of friction is 



2- = - = 0.5542. 

 a y 



REM. In a transverse section in the shape of the half of 

 a regular hexagon, where & = 60, x = 4.39, y = 3.80. 

 width CD = 8.78, and p = 13.16 feet, we have, for the 

 resistance of friction, 



which is less than that found for the above trapezoid. 



121. Uniform Motion. When water flows in an open 

 channel, the velocity continues to increase so long as the 

 accelerating force exceeds the resisting force of friction ; 

 but when these forces are equal to each other, the velocity 

 of the stream becomes uniform. When the velocity is uni- 

 form, the entire head h is employed in overcoming the fric- 

 tion upon the bed. Therefore, the height of the column of 



