Gas in a vacuum?

[DarthDooku]

This thought came to me as i was smoking a cigarette last night. As i blew the smoke out, a big cloud formed. A fan was blowing nearby and slightly contorted the shape of the cloud. I noticed that it took basically the same shape as the gas clouds we have seen that are involved with the birth of a star.

 

It made me think that if there is no air resistance in a vacuum(space), how does a gas cloud spread out and take the form it does.

[Cap'n Refsmmat]

There are still atoms floating around out there, and as the gas has a higher pressure than the surrounding space (which has practically nil) then it tends to spread out.

[Jonfraz]

Does that mean the cloud will eventually dissapate until its evenly diffused, or will its own gravity keep it in cloud form?

[ed84c]

This thought came to me as i was smoking a cigarette last night. As i blew the smoke out' date=' a big cloud formed. A fan was blowing nearby and slightly contorted the shape of the cloud. I noticed that it took basically the same shape as the gas clouds we have seen that are involved with the birth of a star.

 

It made me think that if there is no air resistance in a vacuum(space), how does a gas cloud spread out and take the form it does.[/quote']

 

I think mabye if you gave up smoking it would give you extra time to concider it.

[ydoaPs]

i usualy hear that it spreads out because it spins (which as we know lowers the pressure it would exert on anything, but i's a near vacuum, so there's not much for it to exert pressure on)

[swansont]

i usualy hear that it spreads out because it spins (which as we know lowers the pressure it would exert on anything, but i's a near vacuum, so there's not much for it to exert pressure on)

 

 

How does spinning lower the pressure?

[Primarygun]

Do there any kinetic energy and potential energy exist when there is only one atom or molecule in a bottle of vacuum?

[pulkit]

Do there any kinetic energy and potential energy exist when there is only one atom or molecule in a bottle of vacuum?

Yes of course.

[DarthDooku]

I think mabye if you gave up smoking it would give you extra time to concider it.

 

i am planning on quitting. I have since the day i started. But how does that give me extra time to consider anything. And what good would considering do, when i know nothing about my question.

[ydoaPs]

 

How does spinning lower the pressure?

 

 

bernouli's principle.

[Primarygun]

Yes of course.

Why does the molecule or atom have potential energy?

It doesn't have anything to attract.

[blike]

Let's stay on topic here plleaseee.

[Gant]

Hmmm,,,the star being born would have a gravity,,this gravity would attract the gases,,but also other material,,like rocks,,,lots and lots of rocks,,,all sizes,,,then these rocks also begin to collect together forming new planets,,,all of this swirls around the sun,,,or newly formed sun,,,or newly forming sun. Which then gives it that cool spirlly effect that we all like so much. But i have no source to back my claim up. therefore,,i will call it speculation.

[swansont]

bernouli's principle.

 

I don't see how this applies to the situation. Bernoulli's priciple is that a moving fluid exerts less pressure. Nothing specifically about spinning, and no direct application to a cloud of diffuse gas in a vacuum.

 

It seems like it's diffusion, and nothing more.

[DarthDooku]

Ok, im trying to understand how gas would act in a perfect vacuum. If gas was in a perfect vacuum, wouldnt it just sink to the bottom. And if there was a large source of gravity acting on it wouldnt it move in a straight line directly to the source.

 

So, its generally said that space is a vacuum. But we know that space is not a perfect vacuum. Maybe space shouldnt be thought of as a vacuum. Maybe the atmosphere of space is made of particles too small for us to measure. Therefore, it shouldnt be considered a vacuum, but an entity that is there but acts like a vacuum to things that are on a bigger scale than what the atmosphere is made of.

 

Is that making any sense. I need to read more about the atmosphere of space.

[ydoaPs]

ok, if there was gas in it, it wouldn't be a vacuum. why would it sink to the bottom?

[pulkit]

If gas was in a perfect vacuum, wouldnt it just sink to the bottom

 

If you put a gas where there was once vacuum, it would no longer be vacuum. There is nothing such as a gas in vacuum. As soosn as a gas comes into such a volume, unless it is an enormous quantity, it would merely diffuse out. In case of enormous volumes gravity will come into picture too.

 

Maybe the atmosphere of space is made of particles too small for us to measure

 

Atmosphere means air cover, since space has none, wrong to use that term. Particles too small for us to measure, wats all that about ? Not just imaginative but given todays knowledge of physics probably impossible.

[ydoaPs]

i think u thought it would sink to the bottom because it is denser than a vacuum. there would be nothing for it to be denser than. and that only applies within the effects of gravity, say on a planet. the gas would diffuse, unless it was an enormous ammount, then it would clump togather do to it's own gravity

[swansont]

If you put a gas where there was once vacuum' date=' it would no longer be vacuum. There is nothing such as a gas in vacuum. As soosn as a gas comes into such a volume, unless it is an enormous quantity, it would merely diffuse out. In case of enormous volumes gravity will come into picture too.

[/quote']

 

The notion of vacuum = "perfect vacuum" isn't used very much in science applications. What is used most often is that a vacuum is a region that has a pressure significantly lower than 1 atmosphere.

[pulkit]

Even if you do not take it to be "perfect" vaccuum, given a quantity of gas that is not too enormous, it WILL still diffuse out and not "sink" down.

[ydoaPs]

I don't see how this applies to the situation. Bernoulli's priciple is that a moving fluid exerts less pressure. Nothing specifically about spinning' date=' and no direct application to a cloud of diffuse gas in a vacuum.

 

It seems like it's diffusion, and nothing more.[/quote']

 

i was answering a question

[DarthDooku]

I figured it would be like the experiment with a feather and a marble, or whatever, in a tube that has all the air sucked out. And since there would be no "atmosphere" they both drop at the same speed. Wouldnt a gas be heavy in that situation, and just drop to the bottom. How would it diffuse out if there is nothing to resist its fall. If im not mistaken i do believe that gas does have mass, and would therefore fall to the bottom.

[Sayonara]

i was answering a question

He's disputing your answer.

[SurfSciGuy]

I figured it would be like the experiment with a feather and a marble, or whatever, in a tube that has all the air sucked out. And since there would be no "atmosphere" they both drop at the same speed. Wouldnt a gas be heavy in that situation, and just drop to the bottom. How would it diffuse out if there is nothing to resist its fall. If im not mistaken i do believe that gas does have mass, and would therefore fall to the bottom.

 

The problem is, gas IS atmosphere as such. When we are talking at pressures of the ISM (interstellar medium) which are in the range of 10^-11 to 10^-13 mbar gases no longer behave in the same fashion as they do at atmosphere (i.e. they do not flow). This is because the molecules in the gas are often total independent due to the fact that their mean free path (the average distance between collisions) is huge as their are so few molecule per unit volume. The effect of gravity on individual molecules is small compared to their Kinetic energy (in Ultra High Vacuum Chambers gases are wizzing around at about the speed of sound) so they just bounce around inside the container. In space, however, there is no up or down, so despite the molecules in the ISM having low kinetic energies (T = a few K) they just move around in a random fashion - on the large scale this, however, is expansions as molecule that are head away from a high pressure region are less likely to experience a collision than those heading towards it. As there are few collisions and the gases are very cold - expansion occurs very slowly in space.

[DarthDooku]

The problem is, gas IS atmosphere as such. When we are talking at pressures of the ISM (interstellar medium) which are in the range of 10^-11 to 10^-13 mbar gases no longer behave in the same fashion as they do at atmosphere (i.e. they do not flow). This is because the molecules in the gas are often total independent due to the fact that their mean free path (the average distance between collisions) is huge as their are so few molecule per unit volume. The effect of gravity on individual molecules is small compared to their Kinetic energy (in Ultra High Vacuum Chambers gases are wizzing around at about the speed of sound) so they just bounce around inside the container. In space, however, there is no up or down, so despite the molecules in the ISM having low kinetic energies (T = a few K) they just move around in a random fashion - on the large scale this, however, is expansions as molecule that are head away from a high pressure region are less likely to experience a collision than those heading towards it. As there are few collisions and the gases are very cold - expansion occurs very slowly in space.

 

 

 

Good post. Thats the best explanation so far. Do you know how these stellar nebula's get started? Is there like some central point that sucks everything in, or do the gases just coincidentally run into each other and interact respectively.