Fluid mechanics — definition of lift on an inclined plate Whenever a thin plate is held immersed at some angle to the direction of a moving liquid stream, a pressure distribution acts on it. The component of this resultant pressure that is perpendicular to the free-stream direction is called the aerodynamic (or hydrodynamic) lift. Is this statement correct?

Introduction / Context:
In fluid mechanics and aerodynamics, forces on immersed bodies are resolved into components. Two standard components are drag (along the free stream) and lift (perpendicular to the free stream). A flat or curved plate placed at an angle to the oncoming flow experiences a pressure and shear distribution that results in a net force with these two components.

Given Data / Assumptions:

• An immersed plate is inclined at some angle to the direction of flow.
• The fluid exerts pressure and shear stresses over the plate surface.
• Resultant surface force can be decomposed into components parallel and perpendicular to the free stream.

Concept / Approach:
By definition, the component of the resultant fluid force perpendicular to the undisturbed flow direction is called lift. The component parallel to the undisturbed flow direction is called drag. This definition applies broadly, regardless of whether the plate is a wing, hydrofoil, or a simple immersed flat plate at an angle of attack.

Step-by-Step Solution:
Identify the resultant pressure and shear force on the plate due to the flow.Resolve this resultant into components along and normal to the free stream.Name the along-stream component as drag and the normal component as lift.Hence, the statement given is precisely the definition of lift → it is correct.

Verification / Alternative check:
In wing theory, lift L and drag D are often expressed using coefficients (C_L and C_D) relative to dynamic pressure and planform area. The orientation of these forces is always defined with respect to the free stream, not to the body surface, which confirms the perpendicular component is lift.

Why Other Options Are Wrong:

• False: contradicts the standard definition.
• Only true for very small angles: lift exists for a broad range of angles until stall; the definition does not depend on angle size.
• Laminar vs. turbulent: flow regime changes magnitude, not the definition.

Common Pitfalls:

• Confusing “normal to plate” with “normal to flow.” Lift is defined perpendicular to the free stream, not necessarily normal to the plate surface.

Final Answer:
True