Ask Lemmy

38450 readers

1824 users here now

A Fediverse community for open-ended, thought provoking questions

Rules: (interactive)

1) Be nice and; have fun

Doxxing, trolling, sealioning, racism, toxicity and dog-whistling are not welcomed in AskLemmy. Remember what your mother said: if you can't say something nice, don't say anything at all. In addition, the site-wide Lemmy.world terms of service also apply here. Please familiarize yourself with them

2) All posts must end with a '?'

This is sort of like Jeopardy. Please phrase all post titles in the form of a proper question ending with ?

3) No spam

Please do not flood the community with nonsense. Actual suspected spammers will be banned on site. No astroturfing.

4) NSFW is okay, within reason

Just remember to tag posts with either a content warning or a [NSFW] tag. Overtly sexual posts are not allowed, please direct them to either !asklemmyafterdark@lemmy.world or !asklemmynsfw@lemmynsfw.com. NSFW comments should be restricted to posts tagged [NSFW].

5) This is not a support community.

It is not a place for 'how do I?', type questions. If you have any questions regarding the site itself or would like to report a community, please direct them to Lemmy.world Support or email info@lemmy.world. For other questions check our partnered communities list, or use the search function.

6) No US Politics.

Please don't post about current US Politics. If you need to do this, try !politicaldiscussion@lemmy.world or !askusa@discuss.online

Reminder: The terms of service apply here too.

Partnered Communities:

Logo design credit goes to: tubbadu

founded 2 years ago

MODERATORS

Bluetreefrog@lemmy.world

TheSaneWriter@lemm.ee

TheSaneWriter@lemmy.thesanewriter.com

Asudox@lemmy.world

lemmy_bot@lemmy.world

beefbaby182@lemmy.world

ModeratorCan@lemmy.world

neidu3@sh.itjust.works

asudox@lemmy.asudox.dev

candyman337@lemmy.world

candyman337@sh.itjust.works

Science nerds of Lemmy: Is there an upper limit on the volume of a "confined gas"? (sh.itjust.works)

submitted 5 months ago by captain_aggravated@sh.itjust.works to c/asklemmy@lemmy.world

18 comments fedilink hide all child comments

A lot of the laws of physics I've studied, like Boyle's Law and Charles' Law, describe the behavior of "An ideal confined gas."

I've had to tell several flight students to unlearn what they've learned about that in the meteorology chapter, because, for example, in a confined gas, increasing the temperature causes an increase in pressure while the density stays the same. In the Earth's atmosphere, increasing temperature does nothing to the pressure and decreases the density. Because the Earth's atmosphere isn't "confined," there's no lid, the air is relatively free to change volume. Heat the entire planet up and the atmosphere will just get a little taller.

But, I think, even if we put a magical vacuum tight shell around the planet 200 miles up, making the volume finite, I think the atmosphere would still act like an unconfined gas, because 1. it's so vast that it never homogenizes, parcels of different temperatures, pressures and moisture content take days to slosh across the available space, and 2. the Earth's gravity will cause a pressure gradient; most of the air is at the bottom and if you heat it up, it may not change volume but the pressure at the top will increase.

So I guess there has to be an upper limit to the volume and/or mass of air that can be "confined" and it's somewhere below planetary scale.

you are viewing a single comment's thread
view the rest of the comments

[–] wuphysics87@lemmy.ml 1 points 5 months ago

There are what are called 1st and 2nd order effects. Gravity is first order. The sloshing is second order. So as you say, scaling the model up does make additional factors matter relative to your 1 liter of gas on the table. But it's only the first order effects which make an appreciable difference when looking at it on a planetary scale.

Then if you say want to extend the model to your meteorogical model, you have to say, well... the density of air is different over the ocean because of evaporation. The gulf stream moves clouds consistently this way etc. But those things only matter after you've introduced gravity, and understood the earth's atmosphere as the "gravitational balloon" model. Then you introduce your sloshing to understand the next stage.

This way of thinking about things in terms of leading or second leading order effects when considering systems at varied scales is pretty common in physics.

Btw from lived experience I can tell you the only gulf between you and a 150 level physics class is that you are actually trying to learn it.