|MLA Citation:||Bloomfield, Louis A. "Question 154"|
How Everything Works 21 Jan 2018. 21 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=154>.
Most rocket engines are chemical engines. They combine stored chemical fuels to produce hot, high-pressure gas. This gas is allowed to expand out of a narrow orifice—the throat of the engine's exhaust nozzle. Gases always accelerate toward lower pressure, so the high-pressure gas moves faster and faster as it rushes out of the nozzle. It reaches sonic velocity (the speed of sound) in the nozzle's throat and continues to move faster and faster as it flows out of the nozzle's widening bell. By the time the gas leave the engine completely, it's traveling several thousand meters per second. A liquid fuel rocket has an exhaust velocity of about 4,500 meters per second or about 3 miles per second. Accelerating the gas to this enormous speed takes a huge force—the engine pushes down hard on the gas. The gas pushes back and propels the rocket upward.