Which physical theory explains the generation of thrust by rocket engines, jet engines and deflating balloons?

Newton’s laws of motion

The correct answer is option 1. Newton’s laws of motion.

Newton's third law of motion states that for every action, there is an equal and opposite reaction. This principle applies to the generation of thrust by various propulsion systems such as rocket engines, jet engines, and deflating balloons.

In rocket engines, thrust is generated by expelling high-speed exhaust gases out of the back of the rocket. According to Newton's third law, as the rocket expels gas downward, an equal and opposite force is exerted on the rocket in the opposite direction, propelling it upward.

Similarly, in jet engines, thrust is produced by expelling a high-speed stream of air or combustion gases backward. The reaction force, as per Newton's third law, pushes the aircraft forward.

Even in the case of deflating balloons, when air is released from the balloon, it pushes the air backward, exerting an equal and opposite force that propels the balloon forward.

In all these cases, Newton's third law explains how the generation of thrust occurs through the expulsion of mass or air in one direction, resulting in an equal and opposite reaction that moves the object or vehicle in the opposite direction.