Which physical principle primarily explains the propulsion of rockets?

The propulsion of rockets is primarily explained by Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction. In the context of rocket propulsion, when the rocket engines burn fuel, they expel exhaust gases downwards with a certain force. According to Newton's law, this action of the gases being expelled results in an equal and opposite reaction, which propels the rocket upwards.

This principle is fundamental to the operation of all rocket systems, regardless of their design or fuel type. The thrust generated by the rocket engines is the result of these reaction forces, allowing the rocket to overcome gravitational forces and achieve flight.

The other options relate to different physical phenomena: Bernoulli's principle deals with fluid dynamics and pressure differences in moving fluids, Archimedes' principle pertains to buoyancy in fluids, and conservation of mass is a principle related to mass in closed systems. While these concepts are important in their own contexts, they do not directly explain the propulsion mechanism of rockets in the same way that Newton's Third Law does.