Final answer:
Rockets accelerate forward by Newton's third law, where the backward expulsion of exhaust gases at high velocity creates an equal and opposite reaction force, known as thrust. This action does not depend on external forces, allowing rockets to operate efficiently even in a vacuum.
Step-by-step explanation:
The acceleration of a rocket can be attributed to Newton's third law of motion, which states that to every action, there is an equal and opposite reaction. This fundamental principle explains that rockets move forward by expelling gas backward at high velocity. These gases exert a reaction force, or thrust, on the rocket, propelling it forward. The thrust which pushes the rocket is created by the high-speed ejection of exhaust gases relative to the rocket, and this force increases as the rate at which the rocket's mass is ejected (the burn rate) increases. Additionally, as the rocket consumes fuel and its mass decreases, the acceleration increases, reaching its maximum just before the fuel is exhausted.
Importantly, rockets can operate efficiently in a vacuum where they do not rely on the environment to 'push against', but rather depend solely on the expulsion of mass to generate thrust. The rocket's propulsion is therefore not dependent on an external medium like ground or air, and this is particularly useful in space where there is no atmosphere.