How is velocity pressure defined?

Velocity pressure is defined as the difference between total pressure and static pressure. This measurement is crucial in fluid dynamics and HVAC systems as it indicates the kinetic energy of the fluid flow. When a fluid is moving, its total pressure accounts for both the static pressure (the pressure at rest) and the dynamic pressure (which is related to the fluid's velocity).

By subtracting static pressure from total pressure, you isolate the component of pressure that is specifically due to the motion of the fluid, which is referred to as velocity pressure. This is commonly utilized in airflow calculations to help determine how effectively air is being moved within a duct system or how it interacts with other components.

The other definitions provided do not accurately reflect the nature of velocity pressure. For instance, stating that it is equal to total pressure plus static pressure misrepresents the relationship between these pressure types, as it doesn't align with the principles of fluid dynamics. Similarly, the notion of it being "pressure above total pressure" does not accurately define velocity pressure and could lead to confusion regarding how different pressures interact in a system. Hence, the correct choice is that velocity pressure is indeed equal to total pressure minus static pressure.