In the activity, which variables were kept constant?

In the activity, which variables were kept constant?

• A. Temperature and viscosity
• B. Flow rate and radius
• C. Blood vessel radius and blood vessel length
• D. Pressure and time

Answer: (C)

When studying how flow through a vessel responds to driving conditions, you want to fix the geometry of the path. In Poiseuille-type flow, the flow rate depends very strongly on the radius of the vessel (to the fourth power) and on the vessel length. By keeping the blood vessel radius and blood vessel length constant, you ensure that any observed changes in flow come from other factors like pressure difference or fluid viscosity, not from changes in the tube itself. If the radius or length varied, even small changes would dramatically alter flow, making it impossible to attribute effects to the variable you’re testing. That’s why the constants are the blood vessel radius and blood vessel length.

When studying how flow through a vessel responds to driving conditions, you want to fix the geometry of the path. In Poiseuille-type flow, the flow rate depends very strongly on the radius of the vessel (to the fourth power) and on the vessel length. By keeping the blood vessel radius and blood vessel length constant, you ensure that any observed changes in flow come from other factors like pressure difference or fluid viscosity, not from changes in the tube itself. If the radius or length varied, even small changes would dramatically alter flow, making it impossible to attribute effects to the variable you’re testing. That’s why the constants are the blood vessel radius and blood vessel length.