Which of Newton's Laws best describes a rocket motor's behavior?

The behavior of a rocket motor is best described by Newton's Third Law of Motion: "For every action, there is an equal and opposite reaction." This law is fundamental to the operation of rocket propulsion. When a rocket engine expels gas downwards at high speed, it generates an equal and opposite force that pushes the rocket upwards. This is what enables a rocket to lift off from the ground and ascend into the atmosphere.

The propulsion system works by igniting propellant, which produces high-speed exhaust gases that are forced out of the rocket nozzle. The action of these gases moving downward creates a reaction that propels the rocket in the opposite direction. This relationship between the action of the exhaust and the resulting motion of the rocket exemplifies Newton's Third Law perfectly, making it the correct choice for describing a rocket motor's behavior.

Other laws, while relevant to various aspects of a rocket's motion, do not specifically explain the mechanism of thrust generation as directly as the Third Law. For instance, the First Law addresses the tendency of objects to remain in their current state unless acted upon by an external force, and the Second Law relates to the relationship between force, mass, and acceleration, but neither captures the essence of how rockets achieve thrust through action and