Propulsion and thrust are two closely related terms that are often used interchangeably, but there is a subtle difference between them.

* Propulsion is the generation of a force that moves a body forward or backward.

* Thrust is the force that is generated by propulsion.

In other words, propulsion is the cause, and thrust is the effect.

For example, when a rocket engine burns fuel, it creates hot gases that are expelled out of the nozzle at high speed. The expulsion of these gases generates thrust, which propels the rocket forward.

Another example is when a propeller spins through the air. The spinning of the propeller creates a difference in air pressure between the front and back of the propeller, which generates thrust. This thrust propels the aircraft forward.

In summary, propulsion is the generation of a force that moves a body forward or backward, while thrust is the force that is generated by propulsion.