Reynolds also predicted the friction,  in pipe by measuring the differences of pressure with known length, L.

 

 

 

 

 

 

 

 

 

 

 

 

The friction in circular conduits when flowing full,

     

 

 

 

 

 

 

 

 

 

 

 

The equation is known as the pipe-friction equation and Darcy-Weisbach equation.