Question

Which one of the follflowing is correct?

(a) the frictional resistance is always dependent on the nature of the surface area of contact

(b) the frictional resistance is always independent of the nature of the surface area of contact

(c) the frictional resistance is dependent on the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity

(d) the frictional resistance is independent of the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity

The question was asked by my college director while I was bunking the class.

Question is from Loss of Energy in Pipes topic in section Flow Through Pipes of Fluid Mechanics

Answer 1

The correct answer is (d) the frictional resistance is independent of the nature of the surface area of contact when the liquid flows at a velocity less than the critical velocity

Explanation: Frictional resistance is dependent on the nature of the surface area of contact. But, when the liquid flows at a velocity less than the critical velocity, a thin stationary film of the liquid is formed on the supporting surface. Hence, the frictional resistance becomes independent of the nature of the surface of contact.