Pitot tube usage in fluid mechanics In flowing liquids, a Pitot tube is primarily used to measure which quantity at a point in the stream?

Introduction / Context:
A Pitot tube is a classic point-velocity measuring device used in fluid mechanics and hydraulic engineering. It converts kinetic energy at a point into a measurable pressure rise (stagnation or total pressure), which when compared with static pressure gives the local flow speed. Understanding exactly what the Pitot tube measures helps avoid common selection and interpretation errors in field and laboratory work.

Given Data / Assumptions:

• Incompressible, steady flow at the measuring location.
• Axis of the Pitot tube aligned with the local flow direction (to avoid cosine errors).
• Viscous and probe-tip losses incorporated in an empirical coefficient where needed.

Concept / Approach:
The Pitot tube senses total (stagnation) pressure p_t at its tip and static pressure p_s via side ports or a separate static probe. Bernoulli's principle along a streamline relates velocity head to the difference p_t − p_s. The point velocity V is determined from the pressure difference using V = C * sqrt(2 * (p_t − p_s) / rho), where C is a calibration factor close to unity.

Step-by-Step Solution:

Verification / Alternative check:
In water channels, compare Pitot-derived velocity with average velocity Q/A from volumetric measurements; expect agreement after accounting for profile non-uniformity and calibration.

Why Other Options Are Wrong:
Discharge requires integrating velocity over an area (not measured by a single Pitot reading). Depth is a geometric water-level measure. Static pressure alone is obtained by a piezometer/static tap, not a bare Pitot tip. Therefore, the Pitot tube’s primary purpose is measuring point velocity.

Common Pitfalls:
Misalignment with flow, using the formula without calibration, and applying point velocity directly as section-average velocity without profile correction.

Final Answer:
velocity