Physics · Mechanical Properties Of Fluids · NEET
No. Buoyancy acts even when the fluid and body are still, and it depends on the weight of fluid pushed aside. Dynamic lift only appears when the body is moving through the fluid. If the wing stops moving, dynamic lift becomes zero, but buoyancy would still exist. For a plane, buoyancy is tiny, so dynamic lift does almost all the work.
This comes from Bernoulli's principle. In steady flow, P + (1/2)rho v squared + rho g h stays constant. On a wing the height change is very small, so where the speed v is high, the pressure P must drop to keep the sum constant. So the fast-moving air on top has lower pressure than the slower air below.
A spinning ball drags a thin layer of air around with it. On the side where the dragged air moves the same way as the oncoming air, the total air speed is higher, so pressure is lower. On the other side the speeds oppose, so air is slower and pressure is higher. The ball is pushed from the high-pressure side to the low-pressure side, so it curves. This is called the Magnus effect.
The wing is shaped so its top is more curved and it is often tilted slightly (angle of attack). Air going over the longer, curved top path speeds up, while air below moves slower. Faster air on top means lower pressure on top, so the net pressure force pushes the wing up. This upward force is the dynamic lift.
No. For a ball moving straight without spin, the streamlines are symmetric top and bottom, so the air speed is the same on both sides at matching points. Equal speeds mean equal pressures, so there is no pressure difference and no net upward or downward force. Lift only appears when spin makes the flow unequal.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the force that pushes a moving body sideways or upward as it moves through a fluid. It comes from a pressure difference between two sides caused by different air speeds. Examples are an aeroplane wing and a spinning cricket ball.
Bernoulli's principle. Where fluid speed is high, pressure is low. The side with faster air has lower pressure, so the body is pushed toward that side, giving lift or a curve.
It is the sideways force on a spinning ball moving through air. The spin drags air, making one side faster (low pressure) and the other slower (high pressure), so the ball curves toward the low-pressure side.
The wing shape and tilt make air move faster over the top than the bottom. Faster air on top has lower pressure, so the higher pressure below pushes the wing up. That net upward force is the lift.
No, the top and bottom of a wing are almost at the same height, so the rho g h term is nearly equal on both sides. The lift comes mainly from the speed difference, which changes the (1/2) rho v squared term and so the pressure.
