Ans: To calculate the friction factor we used to use Colebrook equation for fully developed turbulent pipe flow. Also, a graphical method is created by Lewis Moody using the Colebrook equation. However, this method had some disadvantages that Churchill tried to address:

Colebrook equation is implicit in

*Ā 'f'*that is the friction factor appears in both sides of the equation. Whereas the Churchill equation is explicit equation.The Colebrook equation is applicable only to turbulent pipe flow. Whereas the Churchill equation can be used for any Reynolds number, roughness, and transition region.