What principle does jet propulsion rely on?

Jet propulsion relies fundamentally on Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. In the context of jet propulsion, this principle can be observed when a jet engine expels gas at high speed in one direction. As the engine pushes the gas backward, an equal and opposite force propels the aircraft forward. This is the basic operating mechanism of jet engines, which continuously expel exhaust gases to generate thrust.

While Bernoulli's principle describes how the speed of a fluid affects its pressure, and Pascal's law relates to pressure changes in incompressible fluids, these principles do not directly explain the mechanics of propulsion. Similarly, while kinetic energy is important in understanding the motion of the aircraft, it does not capture the fundamental principle governing the forces created by a jet engine. Newton's third law is the most relevant principle as it illustrates the direct relationship between the action of expelling gas and the resulting motion of the aircraft.