Final answer:
A reaction engine operates based on Newton's third law of motion, where the expulsion of hot gases produces an equal and opposite reaction force called thrust, propelling rockets forward. This law underpins the functioning of various engines and biological propulsion systems, and is more efficient in a vacuum.
Step-by-step explanation:
A reaction engine, such as that in rockets, demonstrates Newton's third law of motion, which asserts that for every action, there is an equal and opposite reaction. The reaction engine moves by expelling hot gases in one direction, and in turn, the rocket is pushed in the opposite direction. This is seen when rockets expel gas backward at high velocity, which results in a reaction force called thrust propelling the rocket forward.
The operation of various transportation and propulsion mechanisms, like jet engines, helicopters, and even biological entities like squids, are grounded in this same physical principle. Notably, rockets work better in a vacuum because they don't rely on pushing against the air or ground; instead, the reaction force is more efficiently produced by the expulsion of exhaust gases directly opposing the direction of desired travel.