Which statement about viscosity and flow is true?

Which statement about viscosity and flow is true?

• A. Increasing viscosity decreases flow rate.
• B. Increasing viscosity increases flow rate.
• C. Viscosity has no effect on flow.
• D. Flow rate depends only on radius.

Answer: (A)

Viscosity determines how easily a fluid slides past itself; higher viscosity means more internal friction and greater resistance to motion. In laminar flow through a vessel, the flow rate is inversely related to viscosity: for a given driving pressure gradient, increasing viscosity makes it harder for the fluid to move, so the flow rate drops. Therefore the statement that increasing viscosity decreases flow rate is true. The other ideas miss important points: viscosity does affect flow, so it isn’t zero; increasing viscosity does not increase flow; and while radius strongly influences flow (larger radius raises flow), flow rate also depends on viscosity and other factors like pressure difference and vessel length, not on radius alone.

Viscosity determines how easily a fluid slides past itself; higher viscosity means more internal friction and greater resistance to motion. In laminar flow through a vessel, the flow rate is inversely related to viscosity: for a given driving pressure gradient, increasing viscosity makes it harder for the fluid to move, so the flow rate drops. Therefore the statement that increasing viscosity decreases flow rate is true. The other ideas miss important points: viscosity does affect flow, so it isn’t zero; increasing viscosity does not increase flow; and while radius strongly influences flow (larger radius raises flow), flow rate also depends on viscosity and other factors like pressure difference and vessel length, not on radius alone.