Propulsion is a means of creating force leading to movement. A propulsion system has a source of mechanical power (some type of engine or motor, muscles), and some means of using this power to generate force, such as wheel and axles, propellers, a propulsive nozzle, wings, fins or legs.
Other components such as clutches, gearboxes and so forth may be needed to connect the power source to the force generating component. The term propulsion is derived from two Latin words: pro meaning before or forwards and pellere meaning to drive.
Propulsion is a force that causes movement. The force can be caused by either a differential pressure, or a differential momentum (Newton's second law). In the case of a jet engine, the exhaust velocities are much higher than the inlet velocities, causing a momentum thrust
The word is derived from two Latin words: pro meaning before or forwards and pellere meaning to drive. Propulsion means to push forward or drive an object forward. A propulsion system is a machine that produces thrust to push an object forward. On airplanes, thrust is usually generated through some application of Newton's third law of action and reaction. A gas, or working fluid , is accelerated by the engine, and the reaction to this acceleration produces a force on the engine.
Propulsion moves things like spacecraft or jet planes forward by pushing something out of the back. Think of a balloon that you blow up and then release. The air rushing out of the back pushes the balloon forward. This happens because of a phenomenon described by Sir Issac Newton: "every action has an equal and opposite reaction."