With an increase in the speed of air over a surface, what happens to dynamic and static pressure?

With an increase in the speed of air over a surface, what happens to dynamic and static pressure?

• A. Dynamic pressure increases and static pressure decreases
• B. Both dynamic and static pressures increase
• C. Dynamic pressure decreases while static increases
• D. Both decrease

Answer: (A)

When air speeds up over a surface, Bernoulli’s principle for incompressible, steady flow along a streamline applies: P + 1/2 ρ v^2 remains constant. The dynamic pressure term 1/2 ρ v^2 increases as velocity increases, so to keep the total pressure the same, the static pressure P must decrease. In other words, faster flow over the surface means higher dynamic pressure and lower static pressure. This is why the correct choice states dynamic pressure increases while static pressure decreases.

When air speeds up over a surface, Bernoulli’s principle for incompressible, steady flow along a streamline applies: P + 1/2 ρ v^2 remains constant. The dynamic pressure term 1/2 ρ v^2 increases as velocity increases, so to keep the total pressure the same, the static pressure P must decrease. In other words, faster flow over the surface means higher dynamic pressure and lower static pressure. This is why the correct choice states dynamic pressure increases while static pressure decreases.