Can a rocket move faster than the air it expells?
Yes, a rocket can move faster than the gas it expels. Rockets work on the principle of “Conservation of Momentum”. Momentum is defined as “mass times velocity”. The gas the rocket expels has both mass and velocity in one direction, and this gives the rocket an equal momentum in the other direction. Assume a 100kg (mass) rocket burns 90% of its mass as fuel and that burning this fuel in the engine gives it an exhaust velocity of 10 meters/second. That gives the fuel burned a total momentum (or “impulse”) of 90 kg times 10 m/s = 900 kg*m/s. Since the remaining rocket has to have an equal momentum and the remaining rocket weighs 10 kg, you can divide that into the fuels’ momentum to get a rocket velocity of 900 kg*m/s divided by 10 kg for 90 m/s rocket velocity. Note that this was accomplished with an engine that only imparted 10 m/s velocity to the exhaust gas, but that the final rocket velocity was 9 times that fast.
