Flat Plate in a Stream – Orientation vs pressure/drag When a thin plate is immersed in a liquid with its plane parallel to the flow direction, the pressure force experienced is __________ that for the same plate oriented perpendicular to the flow.

Introduction:
For bluff and streamlined bodies, the orientation relative to the oncoming flow strongly affects pressure distribution and drag. A flat plate parallel to the flow presents a very small projected area normal to the flow, so its form (pressure) drag is much smaller than when the same plate is broadside (perpendicular) to the stream. The question probes this qualitative dependence.

Given Data / Assumptions:

• Steady, uniform approach flow of a single-phase liquid.
• Identical plate, two orientations: parallel vs perpendicular to flow.
• Comparing pressure (form) drag component, not skin friction alone.

Concept / Approach:

Drag on immersed bodies has two principal components: pressure drag from flow separation and wake, and friction drag from viscous shear along the surface. With the plate perpendicular to the flow, the projected frontal area is maximum, separation is large, and form drag dominates. With the plate parallel to flow, the frontal area is minimal, separation is minor, and the main resistance is skin friction along its surfaces, which is typically much less than the broadside form drag for the same speed and fluid properties.

Step-by-Step Solution:

Verification / Alternative check:

Wind-tunnel and water-tunnel measurements consistently show orders-of-magnitude difference in form drag between broadside and edge-wise orientations of thin plates at similar Reynolds numbers.

Why Other Options Are Wrong:

More than / approximately equal to / independent: Contradict well established dependence on frontal area and separation behavior.Reynolds-dependent reversal: While coefficients vary with Reynolds number, the qualitative ordering of broadside vs edge-wise form drag does not invert.

Common Pitfalls:

Confusing total drag with only skin friction; in perpendicular orientation, form drag dominates, leading to much higher overall force.

Final Answer:

less than