The Bernoulli principle describes the inverse relationship between which two factors?

• A. Pressure and Flow
• B. Velocity and Viscosity
• C. Pressure and Fluid Velocity
• D. Volume and Density

Answer: (C)

In Bernoulli's principle, along a streamline in a moving, incompressible fluid, the sum of static pressure and the kinetic energy per unit volume (½ρv²) remains constant. This means that when the fluid speeds up, the static pressure drops; when the speed decreases, the pressure rises. Put simply, there is an inverse relationship between pressure and fluid velocity.

This is why the correct idea is that pressure and fluid velocity move in opposite directions along a streamline. In practical terms, when a vessel narrows and the blood velocity increases, the static pressure drops, creating a pressure gradient that can be detected with Doppler measurements. Viscosity, volume, and density play different roles: viscosity relates to friction and energy losses, while volume and density are separate properties and do not describe the energy trade-off Bernoulli captures.