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How do rocket engines work?



Rocket engines work on Newton's Principle that for every reaction, there is an equal and opposite reaction. When the rocket burns fuel, it's "throwing" the fuel downward, which causes the rocket to rise upward. Think of a firefighter holding a hose with a lot of water coming out of it. If he wouldn't hold it tightly, it would jump around and maybe fly out of his hands. Burning fuel increases the speed at which the fuel is thrown out of the rocket. The faster the fuel comes out of the rocket, the more force there is to push the rocket upward. 

A rocket needs a lot of fuel in order to push it upward, which is one reason why rockets are so big. They need much of that space to carry all that fuel. The usual speed at which burning rocket fuel is pushed out of the rocket is between 5,000 and 10,000 miles per hour (8,046.5 to 16,093 kilometers per hour).