How does a rocket worke?

Answer 1

The critical part of a liquid-fueld rocket that provides it with its ability to "fly" is the combustion chamber, sometimes, but not always, including a shaped nozzle, positioned at the rear (bottom) end of the vehicle. The combustion chamber is open at one end. In its simplest form the chamber is bowl-shaped (a half-sphere) with its open end pointing down, away from the vehicle. The Saturn V, used for the Apollo missions, used this kind of combustion chamber. Combustible liquids are pumped into the chamber. This may consist of a single, essentially self-igniting, liquid, or it may consist of two or more liquids which, when combined, can be made to combust. The Saturvn V used kerosene (the fuel) and liquid oxygen (the oxidizer).

When the engine is "lit" so that the fuel is burning (more like "exploding") inside the combustion chamber it creates tremendous pressures inside the chamber. Some of that pressure is against the upper, inside portion of the combustion chamber, and it is that pressure (force) against the upper inner surface of chamber that propells the rocket. Since the chamber is open at one end the forces in that direction cause the combustion exhaust gases to exit the chamber. This causes an "exhaust plume" out of the back of the rocket engine.

Some have described this as being a situation where the exhaust plume "pushes" the rocket, or that it is the exhaust plume that causes the rocket to move, or that the rocket "rides on top of a trail of fire". But that is not the case and is not a correct way of describing what happens. The exhaust plume does NOT move the rocket. The exhaust plume does NOT cause the rocket to move. Rather, the combustion pressures inside the combustion chamber causes both the rocket motion AND the exhaust motion.

Some have also noted that, since Sir Isaac newton's Third Law Of Motion states that " For every action, there is an equal and opposite reaction ", it is therefore the rapidly exiting gases from the rear of the rocket that cause the rocket to move forward.

Again, this is not a correct description of the situation. Yes, the Third Law of Motion applies to the rocket. Yes, there is both a forward motion of the rocket and a backward motion of the exhaust gases. But it is not correct to say that the one (exhaust gasses) CAUSES the other (the rocket motion). Yes, there is a mathematical, physical relationship between the motion of the exhaust and the motion of the rocket (taking in to account their respective masses), and given a measurement of one you can calculate the other (e.g. knowing the velocity and mass of the exhaust gasses and the mass of the rocket you can calculate the velocity of the rocket). But it is NOT valid to say that the rocket motion is CAUSED BY the exhaust gas' motion.

The correct view on this is that both the motion of the exaust gas and the motion of the rocket are caused by the combustion pressure inside the combustion chamber.