The roughness of the inner liner of a hose is commonly called the ____________________.

• A. Viscosity
• B. Surface roughness
• C. Hydraulic conductivity
• D. Coefficient of friction

Answer: (D)

The key idea is how the wall surface interacts with the flowing fluid to create resistance. The roughness of the inner liner affects how much shear the moving fluid experiences at the boundary, which shows up as friction losses in hose flow. That boundary interaction is quantified by the coefficient of friction—the factor used in equations that relate wall shear to flow conditions and head loss. This term specifically captures the resistance due to the wall, which is what the rough inner surface contributes.

Viscosity is about the fluid’s internal resistance to deformation, not the wall’s roughness. Hydraulic conductivity relates to flow through porous materials, not a smooth hose wall. Surface roughness describes the texture itself, but the practical parameter used in hose and pump calculations to express the wall-induced resistance is the coefficient of friction.