A Pitot tube is used to measure velocity by sensing which quantity, and in which applications is it commonly applied?

• A. It measures dynamic pressure to infer velocity; Common in aircraft, wind tunnels, and ducted air flow.
• B. It measures static pressure to determine altitude; used in submarines.
• C. It measures density of gases; used in pipelines.
• D. It measures temperature.

Answer: (D)

A Pitot tube measures dynamic pressure to infer velocity. It works by facing the oncoming fluid so the flow is brought to a stop inside the tube, creating stagnation pressure. The difference between this stagnation (total) pressure and the ambient static pressure is the dynamic pressure, q = 1/2 ρ v^2. If you know the fluid density, you can solve for velocity with v = sqrt(2q/ρ). In practice, a Pitot-static arrangement separates the total pressure from the static pressure, then uses their difference to compute velocity.

This is why Pitot tubes are widely used in aircraft to determine airspeed, in wind tunnels to map flow velocity, and in ducts for HVAC and industrial flow measurements. They do not directly measure static pressure for altitude, nor do they measure density or temperature.