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Sunday, February 8, 2015

What are the differences between jet airplanes and rockets?

Newton's third law of motion holds good for motion of both jet air planes and rocket engines. They move by expelling hot gases opposite to the direction of desired acceleration. The momentum imparted to the gases is exactly opposite to the momentum imparted to the vehicle.

The biggest difference between a jet engine and a rocket lies in their propulsion systems.

 A jet engine works like this: It sucks in air from the front of the engine. This air is burned with the fuel within the engine. The resulting large mass of gas is ejected towards the rear at high velocity, which both propels the airplane forward, and gets more air sucked into the engine. In normal flight, the engines are used to propel the airplane forward. The actual 'uplift' is gained through the wings using the strong flow of the wind. 

A rocket, in contrast, carries both fuel (which may be solid or liquid) and oxygen. Therefore it does not suck in air from the front. All it does is burn the fuel with the oxygen, and eject it at very high velocities backward. This momentum is used to both lift and propel the rocket. There are no wings for uplift. Any wings are for steering purposes. 

In a nut shell, rocket carries its own supply of oxygen for combustion. A jet engine requires oxygen from the atmosphere for combustion, and so cannot operate in the vacuum of space.