A/An ________ measures the velocity indirectly by measuring the difference between the stagnation and static pressures. 

Explanation:

Pitot Tube:

• A pitot tube also known as a pitot probe is a flow measurement device used to measure fluid flow velocity. The basic pitot tube consists of a tube pointing directly into the fluid flow.  As this tube contains fluid, pressure can be measured; the moving fluid is brought to rest (stagnates) as there is no outlet to allow flow to continue.

This pressure is the stagnation pressure of the fluid, also known as the total pressure of the pitot pressure.

Stagnation pressure = Static pressure + Dynamic pressure

The velocity of the flowing gas in the pitot tube is given by:

\(u = {\sqrt{2(p_t-p_s)\overρ}}\)

where u = Fluid velocity, ρ = Fluid density, pt = Stagnation pressure, ps = Static pressure