The Venturi effect describes...

• A. A device that mixes foam concentrate with water.
• B. A type of nozzle used for fogging.
• C. The increase in velocity with a decrease in pressure when passing through a constricted opening.
• D. A process that seals vapors from fuels.

Answer: (C)

The Venturi effect is about how fluid speed and pressure relate when flow is forced through a narrower section. When a fluid goes through a constricted opening, its velocity increases because the same volume must pass through a smaller area. Because energy is conserved along a streamline (Bernoulli’s principle), that increase in velocity comes with a decrease in static pressure in the constricted area. This pressure change and speed increase are the essence of the Venturi effect and are what such devices exploit to create suction or measure flow.

That’s why the option describing an increase in velocity with a simultaneous drop in pressure as the fluid passes through a constricted opening is the best fit. The other choices describe equipment or processes (foaming, fogging, vapor sealing) that don’t capture the fundamental velocity–pressure relationship of a constricted flow.