Nozzle reaction is explained by the law of physics that states:

The correct answer pertains to Newton's Third Law of Motion, which asserts that for every action, there is an equal and opposite reaction. In the context of nozzle reaction, this principle is crucial for understanding how fluid dynamics operates when water is expelled through a nozzle. When water exits the nozzle at high speed, it creates a force that pushes against the nozzle itself. This reaction force is what propels the nozzle—and thus the entire system—back in the opposite direction to the flow of the water.

This principle of action and reaction explains why nozzle design is so important in various applications, including firefighting equipment and irrigation systems. The efficiency of the nozzle in directing and controlling the flow of water relies fundamentally on this law, making it a foundational concept in fluid mechanics. Understanding this relationship helps operators predict how changes in flow rate or nozzle size can affect performance and stability.