Answer: Conservation of momentum
Notes: The motion of a rocket is an application of Newton’s third law of motion and law of conservation of linear momentum. In a rocket just before launching, the momentum is zero but once the rocket is fired the rocket is fired, it forces a jet of hot gases with a high velocity through the nozzle. The jet of gases acquires a momentum downwards. Hence, the rocket acquires a momentum of equal magnitude in opposite direction. Thus, the rocket moves upwards.
