A rocket or rocket vehicle is a missile, aircraft or other vehicle which obtains thrust by the reaction of the rocket to the ejection of fast moving flui from a rocket engine. Chemical rockets work by the action of hot gas produced by the combustion of the propellant against the inside of combustion chambers and expansion nozzles. This generates forces that accelerate the gas to extremely high speed and exerts a large thrust on the rocket (since every action has an equal and opposite reaction).