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Is it true that space is mostly an empty void?

How do rockets achieve propulsion in the void of space? If there's "nothing", what provides resistance?

  • I've seen an explanation that the engine pushes against the exhaust and that's what creates resistance for propulsion. I can't see that, as the exhaust in the void and again provides no resistance. Can anyone explain this?

  • Answer:

    Newton's third law is usually used to explain rocket thrust in a vaccum. You can also look at it as a conservation of momentum situation. Assume the rocket is stationary in space before the engines are started. I't momentum (mass times velocity) is zero. When the engines are running, mass is being expelled; that mass has momentum, to keep the total momentum zero, the whole rocket has to move in the opposite direction of the expelled mass. The mass of the rocket times its velocity must be equal and opposite (in direction) to the mass times the velocity of the rocket exhaust. So the rocket is propelled forward.

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Newton's second Law of Motion states that "For every action there is an equal but opposite reaction". Gravity acts in this way, while the earth attracts each of us at the surface with a gravitaional force then we too act on the earth with an equal but opposite gravitaional force albeit very small in relationship with the earth's force it remains equal but opposite. Then too in space, if a force is applied in one direction, rg the exhaust gasses of a rocket then those gasses act in an equal but opposite fashion to the rocket therefore propelling the rocket away from the gasses.

Gaz

One of Newton's Laws of Motion is usually stated as "every action has an equal and opposite reaction". A rocket is propelled forward because the gases produced by burning the fuel are expelled out the back. This law is as valid in a total vacuum as it is on Earth. In the case of a rocket in the vacuum of space, as on Earth, the accelerating exhaust leaving the rocket "pushes against" the rocket itself, thus propelling it in the opposite direction.

tonalc1

You can explain it yourself if you take a brick to an ice rink. Stand on the ice and try to move, but nothing happens because the ice is too slippery for your feet to "push against" - don't cheat by pushing at right angles to your skate blades, or by using the little toothed part of them. Now throw the brick along the ice as hard as you can, exactly along the line of your skate blades. The brick goes like the exhaust gas, and you go like the rocket - well, hopefully not so fast, but you will get the idea.

bh8153

"For every action there is an opposite and equal reaction." It doesn't matter what does or does not exist outside of the ship; what matters is what's inside. As the rocket fuel ignites, it creates a force that pushes outward in all directions, pushing the ship away from it except in the direction of the exhaust.

Lord Bearclaw of Gryphon Woods

The "space" your are talking about is NOT a void as there is matter out there. Very, very, very small amounts. But it is there. One type is "solar winds" caused by these small particles. Your Space, or outer space, in which your rocket would be in is not a vacuum. A vacuum is a space absolutely devoid of matter, thus no resistance.

JRC

there doesn't need to be anything - the force of it pushes the ship

forex

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