What is dynamic pressure?

• A. The atmospheric pressure
• B. The force exerted by a static fluid
• C. The force exerted by a fluid in motion
• D. The pressure measured at rest in a tank

Answer: (C)

Dynamic pressure is the part of fluid pressure that comes from the fluid’s motion. It represents the kinetic energy per unit volume carried by the moving fluid, and it can be expressed as q = 1/2 ρ v^2, where ρ is density and v is velocity. In Bernoulli’s sense, total pressure equals static pressure plus dynamic pressure, so the faster the fluid moves (or the denser it is), the greater the dynamic pressure.

The correct description focuses on the pressure arising specifically from motion, i.e., the force per unit area due to the moving fluid. It’s not the ambient atmospheric pressure, and not the static pressure you get from a fluid at rest or from depth. A practical takeaway is that a moving fluid exerts more pressure on a surface than a stationary one with the same static conditions, quantified by dynamic pressure. For example, air flowing over a wing increases the surface pressure due to its motion, which is captured by dynamic pressure. A pitot tube measures total pressure, and subtracting static pressure gives dynamic pressure.