FAA Powerplant Written Practice Test

What fundamental principle allows a propeller to produce thrust?

1. Conservation of energy

2. Newton's third law of motion

3. Bernoulli's principle

4. Archimedes' principle

The correct answer is: Newton's third law of motion

The fundamental principle that enables a propeller to produce thrust is Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. When a propeller spins, it pushes air backwards, which generates a forward thrust due to the reaction of the air being displaced. This action-reaction interaction is what propels the aircraft forward. In the context of thrust generation, as the blades of the propeller rotate, they create a difference in pressure between the upper and lower surfaces of the blades, which can also be explained by Bernoulli's principle. However, it is the reactive force resulting from the action of pushing air backwards that is most directly described by Newton's third law and is critical for understanding how thrust is created.