Final answer:
Air moves faster over the upper surface of an aerofoil because its design causes a longer path for airflow, leading to reduced pressure and increased velocity on top in accordance with Bernoulli's principle, which produces lift.
Step-by-step explanation:
The air moves faster on the top of an aerofoil due to the implementation of Bernoulli's principle combined with the physical geometry of the wing. An aerofoil is designed such that its upper surface is more curved, or often longer, than the bottom surface. This design causes the air to spread out more over the top surface, speeding up to fill the increased space and reduce pressure, according to Bernoulli's principle, which states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Moreover, the wing's tilt, or angle of attack, directs air downwards, which by Newton's third law, results in an upward lift. This demonstrates how the design of the aerofoil is key to ensuring that air moves effectively over the wing to create sufficient lift. It's important to note that while Bernoulli's principle provides some insight into how lift is generated, lift also arises from other factors such as wing shape, angle of attack, and airflow around the wing which can create turbulence.