How does jet engine/rocket thrust work? There is no atmosphere in outter space !?

Question

If the exhaust depends on pushing against the atmosphere, how can it work in outter space ?

Answer 1

Both work by the Law of Conservation of Momentum. Neither has anything to do with "pushing against the atmosphere".

When motionless, the jet/rocket has zero momentum:

Momentum = mass * velocity

If Velocity = 0, then Mass * 0 = 0. that is, an object at rest has no momentum.

The fuel used in either a jet or rocket engine has mass, as does the rocket/jet being propelled. When burned, the fuel generates hot exhaust gases (which have mass) being forced out the back end of the engine. Since the gases have low mass, but high velocity, they have momentum. In order to conserve momentum in the entire system, the jet/rocket (which has a high mass) starts moving in the opposite direction. At first, this motion is slow, but under the continuous burning of fuel, the velocity of the rocket/jet increases as more mass of fuel/exhaust is farced out the exhaust. In addition, the acceleration is enhanced by the fact that the rocket/jet is losing mass (the fuel being burned).

No pushing against the atmosphere is involved. In fact, the hot exhaust gases are pushing against the jet/rocket! And that, in essence, is Newton's Third Law -- for every action, there is an equal and opposite reaction.

Answer 2

No... pushing against something isn't necessary.

Try this. Sit in a swing, holding a brick. Throw the brick out in front of you. As a result, you're body swings a little in the opposite direction - and the brick hasn't pushed against anything.

Now (don't do this at home) Pretend the brick is C-4 (and explosive). Instead of throwing the brick, detonate it. The blast will likely push you OFF the swing - but again, the blast itself didn't push against anything on the other side to cause the reaction.

Now, for something in the middle. A controlled blast - like a thruster or a rocket engine - burns fuel at a precise level, causing the reaction to push you in the opposite direction. For you to move, there just has to be a force exerted to make it happen - and that doesn't require anything to 'push' against.

Answer 3

Jet engines do not work in outer space as they need air coming into them to burn their fuel.
Rocket engines work not by pushing against the air but by pushing against the mass of the exhaust.
The rocket exhaust is moving much faster than the rocket.
Momentum is the multiplication of mass times velocity.
Newton's third law of motion is that for every action there is an equal reaction in the opposite direction.

Answer 4

YOU ALWAYS NEED AN EXTERNAL MASS FOR AN ENGINE TO PUSH AGAINST (not the mass the engine is strapped to).

A boat engine uses a propeller to push against water, a car engine uses tires to push against the land, a helicopter uses rotors to push against the atmosphere, a bi-plane uses rotors to push against the atmosphere, a rocket engine uses jet exhaust nozzle to push against the atmosphere but NASA says their magical engines do not need to push against any mass that is exterior to themselves. That is impossible folks.

These poor brainwashed people actually want you to believe that the tremendous amount of air being shot out the back of a rocket engine (thrust) does not push against the atmosphere to move the rocket? How funny! Could someone please tell me how that much thrust would not push against the atmosphere? Has everyone been fooled and brainwashed by NASA regarding how thrust works and why NASA is a bunch of liars trying to protect their Moon Walk lies? One cannot get anymore brainwashed to actually believe that thrust does not push against the atmosphere. Amazing divorce from reason, logic and reality. I guess a hovercraft does not use it's thrust to push against the ground to hover or an Airboat does not use its giant fan to push against the atmosphere to move? Get real people.

No wonder there were no craters under the Lunar Lander engines when it supposedly landed on the Moon, since THRUST appears not to be needed for these magical NASA engines.

Answer 5

By Newton's Third law - To every action there is an equal and oposite reaction.

The force of discharge from the rocket exhaust will propel the rocket forward. It has nothing to do with pushing against anything.

Answer 6

The exhaust doesn't push against air, the earth or the atmosphere, it just pushes.