Forces on an Inclined Plate in a Stream – Naming the Components When a flat plate is immersed at an angle to a liquid stream, the resultant pressure on the plate can be decomposed into components. The component along the direction of flow is called drag; the perpendicular component is called lift.

Introduction:
External flows over bodies generate forces that engineers decompose into lift (normal to flow) and drag (along flow). Correct terminology is crucial in aerodynamics, hydraulic structures, and particulate transport.

Given Data / Assumptions:

• Uniform approach flow over a thin plate at angle of attack.
• Reynolds number sufficiently high to permit boundary-layer formation.
• Pressure and viscous shear both contribute to resultant force.

Concept / Approach:

The resultant hydrodynamic force is the vector sum of pressure (form) drag and shear (skin-friction) forces. Its decomposition into streamwise (drag) and normal (lift) components defines performance metrics like drag coefficient and lift coefficient.

Step-by-Step Solution:

Verification / Alternative check:

Wind-tunnel balances directly report drag and lift components relative to the free-stream direction, validating the definitions.

Why Other Options Are Wrong:

Lift: By definition the normal component, not along the flow. Stagnation pressure: A local pressure at zero relative velocity point, not a net force component. Bulk modulus: Material property unrelated to external flow force decomposition. Skin friction only: Drag includes both pressure and shear contributions.

Common Pitfalls:

Assuming drag arises only from viscosity (skin-friction) and ignoring pressure (form) drag; misaligning axes so components are mislabeled.

Final Answer:

drag