Which statement correctly describes the Venturi effect?

• A. It describes a decrease in velocity as a fluid passes through a constriction.
• B. It describes an increase in pressure as velocity increases.
• C. It describes that velocity decreases when passing through a reduced opening.
• D. It describes an increase in velocity and a decrease in pressure as the fluid passes through a restricted opening.

Answer: (D)

When a fluid is forced through a restricted opening, its speed increases while its static pressure decreases. This happens because the flow must conserve mass as the cross-sectional area shrinks, so velocity goes up (continuity). Bernoulli’s principle then implies that the rise in kinetic energy comes with a drop in pressure to keep total energy constant for incompressible, steady flow. That combination—increased velocity and decreased pressure in the restricted section—captures the Venturi effect. The other statements contradict these fundamental relationships: velocity cannot decrease in a constriction, and increasing velocity does not come with higher pressure. The Venturi effect explains why devices like flow meters rely on the pressure drop in the narrow part to measure flow.