In the early days of rocketry, some people claimed that rockets couldn't fly in outer space as there was no air for the rockets to push against. Suppose you were an early investigator in the field of rocketry and met someone who made this argument. How would you convince the person that rockets could travel in space? Explain in detail.

If I were to convince the person that rockets could travel in space, I would use conservation of momentum (For two or more bodies in an isolated system acting upon each other, their total momentum remains constant unless an external force is applied. Therefore, momentum can neither be created nor destroyed) and Newton's third law of motion (Every action produces an equal and opposite reaction.)

Explanation:

We know that a rocket burns fuel and expels the exhaust gases that are produced though a nozzle. We can actually manipulate these expelled exhaust gases. The expelled gases exert an equal and opposite force on the rocket, thereby propelling the rocket forward in the opposite direction of the release of gas. Newton's third law is seen in action here.

According to the law of conservation, the momentum is zero since the rocket and the fuel are initially at rest. In order to conserve the momentum since it can not be created nor destroyed, once the combustion of the fuel takes place which results in expulsion of gases, the system will need an equal but opposit change in momentum for the rocket, thereby moving the rocket.