What makes a rocket move in space? There is no air to push against.?

Question

There is no air in space. For anything to move it needs to push against something. So when a rocket is in space and in a vacuum what does the rocket push against? Its own gases?

Answer 1

The rocket in a vacuum pushes against itself! As the gases escape the rocket motor they push against the motor itself, hence there is movement. A rocket is impeded by the atmosphere, so it is more efficient in a vacuum.

It is NOT true that rockets cannot go faster than the exhaust gases (this was implied by one of the other answerers). The velocity of exhaust gases of even the most modern rockets fall far short of escape velocity or of orbital velocity (yet the rockets and payloads achieve those velocities). The exhaust gases do not "know" how fast the rocket is going at any one time....they still come out of the motor at the same velocity relative to the rocket. The longer the motor fires the faster the rocket will go (neglecting relativity aspects, of course).

Answer 2

Conservation of momentum.

The total momentum of the system (the spacecraft and the expelled gases) must stay constant. If the gases are pushed out the back of the spacecraft, then the spacecraft has to move the opposite direction with the same momentum.

Momentum is:

p = mv
where m is mass and v is velocity.
If you take the mass of the gases expelled and mutliply by the speed that the gases are expelled at, you determine how much momentum the departing gases had.

The spacecraft has to have the same momentum in the opposite direction to keep the overall balance. Divide the spacecraft's momentum by the mass and you get the speed of the spacecraft.

Obviously, the spacecraft moves much slower than the gases that were expelled since the spacecraft has so much more mass. That's why the expelled mass has to be shot out the back in a combustible reaction that sends the gas out the back at a very high velocity.

Answer 3

You know how an artillery piece leaps backwards when it fires? It would do that even if there wasn't any air around. That's exactly how a rocket works, except instead of the shell, it emits the high-speed gaseous exhaust.

That's why rockets always burn fuel so quickly - you need to send a lot of gas in the other direction to make something that heavy go fast enough.

Answer 4

That's why it is a rocket. The burning fuel creates gas, which escapes down the nozzle. The gas moves backwards, so the rocket must move forward.

Answer 5

Action and reaction. The burned gasses shoot out of the rocket engine in one direction (even gas weighs something) and the rocket moves in the other.

Answer 6

Rockets use Issac Newton's third law of physics every action has an equal opposite reaction.

Answer 7

once the rocket gets rid of the thing that launches them it has fuel that chemically so it well move. the gas but off makes it move, because there is no air in space

Answer 8

1) Newton's Third Law
2) If there's no air to push against it, the easier it is to propel the rocket.

Answer 9

Oxidative Combustion Reactions

to get to space, nothing required once in orbit

Answer 10

well it uses thrusters to move using fuel like the space shuttles but when you get in orbit around a planet you don't need thrusters to keep in orbit because the gravity keeps you orbiting around that planet you need them when you want to get out of orbit though