About Bernoulli’s principle

Critical thinking Use Bernoulli’s principle to explain why pressure in a fluid decreases within a pipe as its radius decreases.

Answer:  From the continuity equation, the speed of a fluid in a narrowing pipe increases. This increase in speed indicates that the fluid is being accelerated forward by a net force, and that this force arises from a difference in pressure within the fluid. Because the force is in the forward direction, the pressure at the front of the fluid must be lower than the pressure behind it. Thus pressure within the fluid decreases as the fluid’s speed increases.

Critical thinking Use Bernoulli’s principle to explain how an airplane achieves lift by moving forward at high speed. (answer on your notebook).

Answer: As the airplane moves forward with greater speed, the flow of air around the airplane wing reduces the pressure of the air. The wing is shaped so that air flows more rapidly over the wing than under it, and therefore causes the pressure above the wing to be lower than the pressure below it. The greater pressure under the wing raises the wing, causing the airplane to lift.