Which principle explains why airplanes are able to achieve lift?

Airplanes achieve lift primarily due to Bernoulli's Principle, which relates to the behavior of fluid dynamics. This principle states that as the velocity of a fluid increases, the pressure within that fluid decreases.

In the case of an airplane wing, known as an airfoil, the shape of the wing is designed to create a difference in airflow velocities above and below the wing. When the airplane moves forward, air splits to flow over and under the wing. The air moves faster over the curved upper surface, resulting in lower pressure compared to the higher pressure generated below the flat or slightly curved bottom surface. This pressure difference creates an upward lifting force on the wing, allowing the airplane to rise off the ground.

While other principles like Newton's Third Law of Motion, which explains action and reaction forces, do play a role in the lift generated by the wings through the downward deflection of air, it is Bernoulli's Principle that directly explains the pressure differential that leads to lift in a way that is fundamental to the function of airplane wings.

In summary, Bernoulli's Principle is essential for understanding how the shape and airflow around the wings contribute to creating lift, making it the correct answer to the question.