Which statement correctly distinguishes static pressure from total pressure in moving fluids?

Which statement correctly distinguishes static pressure from total pressure in moving fluids?

• A. Static pressure is the fluid pressure at a point; total pressure equals static pressure plus dynamic (velocity) head.
• B. Static pressure plus dynamic head equals atmospheric pressure.
• C. Total pressure is the static pressure measured with velocity ignored.
• D. Total pressure equals static pressure minus dynamic head.

Answer: (A)

In moving fluids, total pressure combines the pressure energy with the energy due to the fluid’s motion. The static pressure is the pressure you measure at a point, while the dynamic (velocity) head is ½ρv², representing the kinetic energy per unit volume. The total pressure (stagnation pressure) is the sum of these two: p + ½ρv². This matches Bernoulli’s idea that along a streamline, p + ½ρv² (ignoring elevation changes) stays constant. That’s why the statement is correct: total pressure equals static pressure plus dynamic head. The other options misstate the relationship—dynamic head isn’t added to reach atmospheric pressure, total pressure isn’t static pressure with velocity ignored, and it isn’t static pressure minus dynamic head.

In moving fluids, total pressure combines the pressure energy with the energy due to the fluid’s motion. The static pressure is the pressure you measure at a point, while the dynamic (velocity) head is ½ρv², representing the kinetic energy per unit volume. The total pressure (stagnation pressure) is the sum of these two: p + ½ρv². This matches Bernoulli’s idea that along a streamline, p + ½ρv² (ignoring elevation changes) stays constant.

That’s why the statement is correct: total pressure equals static pressure plus dynamic head. The other options misstate the relationship—dynamic head isn’t added to reach atmospheric pressure, total pressure isn’t static pressure with velocity ignored, and it isn’t static pressure minus dynamic head.