Fluid properties – comparing dynamic viscosity At ordinary temperatures, the dynamic viscosity of water is __________ that of mercury.

Introduction / Context:
Viscosity measures a fluid’s resistance to shear. Comparing fluids helps anticipate flow regimes and head losses. Water and mercury are common reference liquids with different molecular interactions and viscosities.

Given Data / Assumptions:

• Room temperature conditions (around 20 °C).
• Dynamic viscosity μ is considered (not kinematic).
• Both liquids are pure and standard.

Concept / Approach:
At ~20 °C, water has μ ≈ 1 mPa·s, while mercury has μ ≈ 1.5–1.6 mPa·s. Hence, water is less viscous than mercury. Kinematic viscosity ν = μ/ρ would differ even more due to mercury’s very high density, but the question explicitly refers to viscosity (μ).

Step-by-Step Reasoning:

Verification / Alternative check:
Handbooks provide tabulated μ for common fluids; values confirm the same ordering across a reasonable temperature range near ambient.

Why Other Options Are Wrong:

• Higher / same: contradict empirical data.
• “Undefined because viscosity has no units”: incorrect; dynamic viscosity has SI units Pa·s.

Common Pitfalls:
Confusing dynamic viscosity with kinematic viscosity; mercury’s ν is smaller than water’s because of its very high density, but μ is larger.

Final Answer:
lower than