Which statement best describes the relationship between viscosity and flow rate?

Which statement best describes the relationship between viscosity and flow rate?

• A. Higher viscosity increases flow rate
• B. Higher viscosity decreases flow rate
• C. Viscosity does not affect flow rate
• D. Viscosity only affects flow rate at high pressures

Answer: (B)

Viscosity is the fluid’s internal friction that resists motion. When you push fluid through a tube, the flow rate depends on how strongly the fluid resists shearing versus how much driving pressure you apply. The higher the viscosity, the more the fluid resists movement, so the flow rate drops under the same driving conditions. In laminar tube flow, a key relationship is that the flow rate Q is proportional to the pressure difference ΔP and to r^4, but inversely proportional to viscosity μ and the length L. So, for fixed ΔP, radius, and length, increasing viscosity reduces the flow rate. A concrete takeaway: doubling viscosity roughly reduces the flow rate by about half if everything else stays the same. Thus, the statement that higher viscosity decreases flow rate best describes the relationship. If you raise the driving pressure, you can overcome some of that resistance, but the underlying trend remains that viscosity acts to slow flow.

Viscosity is the fluid’s internal friction that resists motion. When you push fluid through a tube, the flow rate depends on how strongly the fluid resists shearing versus how much driving pressure you apply. The higher the viscosity, the more the fluid resists movement, so the flow rate drops under the same driving conditions.

In laminar tube flow, a key relationship is that the flow rate Q is proportional to the pressure difference ΔP and to r^4, but inversely proportional to viscosity μ and the length L. So, for fixed ΔP, radius, and length, increasing viscosity reduces the flow rate. A concrete takeaway: doubling viscosity roughly reduces the flow rate by about half if everything else stays the same.

Thus, the statement that higher viscosity decreases flow rate best describes the relationship. If you raise the driving pressure, you can overcome some of that resistance, but the underlying trend remains that viscosity acts to slow flow.