Bernoulli's Principle explains how pressure in a moving fluid varies with what?

• A. Pressure increases with speed.
• B. Pressure decreases as speed increases.
• C. Pressure remains constant.
• D. Pressure depends on temperature.

Answer: (B)

In Bernoulli's principle, for steady, incompressible flow along a streamline, the total mechanical energy per unit volume stays the same. This means static pressure and dynamic pressure (related to speed) trade off: as the flow speeds up, the static pressure must fall to keep the energy balance. So pressure decreases as speed increases.

This is why faster flow in a constricted region has lower pressure, which also helps explain lift on an airfoil and the functioning of devices like venturi tubes. The relation isn’t that pressure rises with speed, and pressure isn’t constant if the speed changes. Temperature isn’t the direct factor in this energy balance, though it can influence density and other aspects of the flow.