Why doesn't the earth's atmosphere float out to space?
I am told that space is a near vacuum so, why isn't the atmosphere just sucked out into nothingness? Please don't tell me it's gravity because I know that if you induce a vaccuum here on earth and then expose it to the air, air will rush to fill the void. Therefore, it would seem that gravity has no affect.
2007-07-19T15:29:12Z
OK. So from what I am seeing in the replies so far, it leads me to believe that if one should open up a window on the space shuttle or international space station then, nothing would happen because the air and the vehicle are both falling at the same rate around the earth. If this is not the case, then please explain.
Troasa2007-07-23T13:38:02Z
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OK I won't start with the word gravity....hmmm.... What is atmosphere? Gases. Earth's atmosphere consists mostly of the gases nitrogen, oxygen, argon, and carbon dioxide. These gases are composed of atoms. These atoms have weight. They are not simply "air". We don't yet know what gravity is but we can define it because we know how it operates. Gravity is the force of attraction between any two bodies or particles proportional to their masses. Earth has a large mass compared to a nitrogen atom. Therefore, the nitrogen atom is held close to Earth. It was initially released from the Earth and could not escape the gravitational field. It is not directly on the surface for the same reason that you can throw a ball into the air. There is no definite boundary between the atmosphere and outer space. It slowly becomes thinner and gradually fades into space. It's density decreasing with it's distance from Earth. In similar ways, our moon has very little atmosphere because it's mass is low as it lacks iron in it's core. And asteroids are unable to hold atmosphere because they lack enough mass. Jupiter, because it's mass is so large, is able to hold heavier atoms in it's atmosphere such as sulfur. So the size and composition of an object's atmosphere is related to it's mass. The ability of a body to attract another body or particle is also related to distance. In fact the inverse square rule. Twice as far away, it has only 1/2 the pull. I believe this is what we use the word vacuum for in space. Places where the attraction from other bodies is so weak that there is in relative terms no pull at all and thus is called a vacuum. The term vacuum is in fact philosophical and has never been demonstrated or observed in practice. Interstellar space is not void of matter. It contains hydrogen atoms, photons, electrons, neutrinos, and background radiation. Truly, most of the mass of the Universe is found in "empty" space. I believe there may be some confusion between the term vacuum and what you are referring to which would be better termed pressure. As a pressurized airplane or space suit. Whereas any released gas would flow to the area of less pressure.
The earth's gravity is so heavy that it keeps the atmosphere in. The atmosphere is about .2% as thick as the Earth. A small vaccuum sucks in the air because the air pressure outside the vaccuum pushes the air in.
It is still gravity that holds the atmosphere even if you don't want it to be.
However at the edges of the atmosphere where the gravity is weak the lighter elements like hydrogen and helium do actually escape and get blown out into space by the solar wind.
If we didn't have a magnetic field then there would be a lot less atmosphere because it deflects the solar wind and saves our air. Otherwise we would have a planet like Mars without enough air left to breath.
In physics I learned there is no such thing as "sucking" A vacuum cleaner works by using a pump to lower the air pressure inside, then higher pressure air outside PUSHES its way into the cleaner. In a vacuum, a vacuum cleaner would not work because the outside pressure is already zero. Suction cups wouldn't work either. The cup does not pull itself to the surface, outside air pressure PUSHES the suction cup to the surface. In a vacuum, it wouldn't stick at all. So the vacuum of space does not pull, the air tries to push its way up from Earth, but gravity keeps pulling it back. The result is the air can sort of puff up a few miles and no more.
You are missing a key element in your comparison of a vacuum on Earth. The reason a vacuum on Earth refills with air is air pressure, about 30 pounds per square inch. This air pressure is caused by the wieght of the air in our atmosphere pushing down due to...you guessed it...gravity. The reason that air gets thinner at high altitude is that there is less...pressure. Less air is pushing down from on top. At a certain point, the air is so thin that we can't breathe, but it's still there, and held in place by gravity. All of this happens within the "gravity well" of Earth.