Final answer:
Bernoulli's principle is used to describe lift in fluids, particularly in the context of air over airplane wings or sails, where it generates lift or thrust. Archimedes' principle, on the other hand, explains the buoyant force and is not the correct principle for describing lift.
Step-by-step explanation:
The principle used to describe lift is known as Bernoulli's principle. According to Bernoulli's principle, an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. This principle is applied to aircraft wings and sailboats' sails, where the difference in pressure above and below the wing or sail generates lift or thrust.
While Archimedes' principle is also related to forces in fluids, it specifically deals with the buoyant force on an object submerged in a fluid, stating that the buoyant force is equal to the weight of the fluid that the object displaces. This is different from Bernoulli's principle, which helps explain how variation in fluid speed contributes to lift.