What best describes how Bernoulli's principle relates to lift and its limitations in real flows?

• A. Lift arises from pressure differences due to velocity changes, and Bernoulli's principle assumes inviscid, steady, incompressible flow; real flows involve viscosity, separation, and unsteadiness.
• B. Lift is caused primarily by gravity and buoyancy.
• C. Bernoulli's principle applies equally well to all real flows without limitations.
• D. Pressure and velocity have no relation to lift.

Answer: (A)

Lift comes from a pressure difference between the wing’s upper and lower surfaces created by how the flow is directed around the wing. Bernoulli’s principle connects pressure and velocity for an ideal, steady, incompressible, inviscid flow along a streamline, so it helps explain why speeds are often higher over the top and pressures lower there. But real flows around a wing aren’t ideal: viscosity creates boundary layers that stick to surfaces, flow can separate especially at higher angles of attack, and the flow can be unsteady or compressible. These effects alter the pressure field in ways that the simple Bernoulli relation doesn’t capture, so you can’t use Bernoulli alone to predict lift in all situations. In practice, lift arises from the overall pressure distribution shaped by wing geometry and angle of attack, which is influenced by viscous effects and possible flow separation, while the idea of deflecting air downward (momentum change) provides a complementary way to understand where that pressure difference comes from.