Section 4: Soil and Water Conservation Engineering
Fluid Mechanics
Subtopic: Ideal and real fluids, properties of fluids
Question Statement:
The viscosity of a newtonian fluid depends primarily on X and to a lesser degree on Y. X and Y are
Options:
(A) X = temperature, Y = flow velocity
(B) X = flow velocity, Y = pressure
(C) X = temperature, Y = pressure
(D) X = roughness of the surface across which the fluid flows, Y = flow velocity
Official Answer Key:
C
Step-by-Step Solution & Explanation
Dynamic viscosity of a Newtonian fluid is, by definition, a property of the fluid itself (a function of its molecular structure/intermolecular forces) and is essentially independent of the flow field — it does not depend on velocity or surface roughness at all. It is strongly dependent on temperature (viscosity drops sharply with rising temperature for liquids, rises for gases) and only weakly dependent on pressure (significant only at very high pressures). This matches option (C): X = temperature (primary), Y = pressure (secondary).
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