Final answer:
The claim that multi-stage rockets require more force to keep the rocket moving is false. Rockets move by expelling gas backward, and once in motion, no additional external force is required in space due to Newton's first law.
Step-by-step explanation:
The statement that multi-stage rockets require more force to keep the rocket moving is false. The fundamental principle of rocket motion is explained by Newton's third law, which states that for every action, there is an equal and opposite reaction. Rockets move by expelling gas in the backward direction at high velocity, and this action creates an opposite reaction that pushes the rocket forward. This is an internal force; no additional external force is required to maintain motion once the rocket is underway in the vacuum of space.
According to Newton's first law, once a rocket has escaped Earth's gravitational pull and is moving through the vacuum of space, it will continue to travel in a straight line until acted upon by another force, which could be the gravitational pull of another celestial body or the effect of solar wind on a solar sail craft.
In the case of multi-stage rockets, the subsequent stages ignite after the earlier ones have burned out, which allows the rocket to sustain its acceleration out of Earth's gravity well without necessarily requiring more force. The sequential activation of different stages is designed to provide the right amount of velocity at the right time to send payloads into space efficiently.