Jet propulsion

Jet propulsion produces thrust by accelerating and expelling a fluid mass. Its reaction force moves the vehicle in the opposite direction.

Newton's third law: Forces between two bodies are equal in magnitude and opposite in direction. The expelled fluid pushes back on the vehicle with an opposing force.
Conservation of momentum: The principle that the total momentum of an isolated system remains constant. It gives the system-level account of vehicle motion and exhaust motion together.
Turbojet: A gas-turbine engine that produces thrust mainly by accelerating a high-speed exhaust jet. It is the classic air-breathing implementation of jet propulsion.
Propeller: A rotating device with blades that produces thrust by accelerating a surrounding fluid. Propellers accelerate a large mass of air modestly, unlike fast exhaust jets.
Momentum thrust: Thrust generated by changing the momentum of a flowing mass of fluid. It expresses jet propulsion as the momentum gained by expelled fluid.
Fluid mechanics: The study of fluids at rest and in motion, including their forces and flows. Jet propulsion depends on controlling moving liquids or gases.
Turbofan: A gas-turbine engine whose fan accelerates both bypass air and core flow. Most modern airliners use this efficient form of jet propulsion.
Electric propulsion: Spacecraft propulsion that accelerates charged particles using electrical energy. It produces very low thrust with high propellant efficiency, unlike typical chemical jets.
Nozzle: A shaped passage that controls and accelerates fluid flow. The nozzle converts pressure and thermal energy into a faster exhaust jet.
Drag equation: An equation relating drag force to fluid density, speed, reference area, and drag coefficient. Thrust must overcome aerodynamic drag for an aircraft to accelerate or maintain speed.

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