Density

[jo90]

Does a helium baloon deflate before an ordinary carbon dioxide baloon? If you had two baloons (one helium filled and the other blown up by breath) which would deflate first?
Sorry, this is my 12 year old's science question
What happened to the good old days when you were told to read up about all the things they couldn't explain to you
Anyway, back to density, please help - i'm 50 but I really want to help my 12 year old.

[MrsJo49155]

I guess it depends how well you tie them...we actually have a small helium gromit balloon which my son bought at a fairground in 1997 which is still going...but them again it is a metalic balloon rather than a latex one!

[brachiopod]

TEST (sorry, it doesn't want to let me post abig answer)

TEST

[brachiopod]

Wow! a carbon dioxide ballon! That will go down well!

Sorry, jo90, let me start again.

A ballon, being a skin of synthetic rubber, is not a perfect container of air. Now, on a short timescale, they are fine, they can hold the air you blow into them (unlike, say, the mesh net bag your fruit or onions come in).

[brachiopod]

However, over time, they do deflate. This is not "air being lost through the knot", but through the ballon skin itself. This is because the ballon skin is a semi-permeable membrane.

Think about one of those fruit / onion bags made of netting - you want, (say), an onion or a tangerine so tear a hole in the net and pull one out. When you put the bag away, the items jiggle about, but don't fall out until you just-about reach the cupboard, when one of your onions/tangerines falls out and rolls under the sideboard / dogbasket / Swedish au pair etc.etc.

[brachiopod]

Well, the molecules of air in a balloon are all whizzing around, banging into the sides of the balloon. Most of the time, they rebound off the "net" structure of the rubber, however, occasionally, a molecule of air will hit the "hole" of the ballon-rubber net and escape. Over time, more and more molecules of gas escape in this way, so the ballon eventually deflates.

[brachiopod]

With a helium balloon, the gas molecules (or atoms in helium's case, as it is an inert gas) are much smaller, and less dense ("lighter") than those that make up the constituents of air. They also move faster, thus the chances of them hitting a "hole" in the "net" of the ballon skin are much higher - hence the helium ballon deflates a lot quicker than the air balloon.

[brachiopod]

Sorry about the disjointed posts - it just wouldn't let me post a long answer (even under 2000 words)

The analogy is like a net bag filled with tangerines (air ballon) and the other (same sized net) filled with grapes or even peas.(helium ballon)

Finally, a true 'carbon dioxide' balloon is great fun. Exhaled breath only contains, at most, about 4% CO2, so it is still mainly nitrogen, with a little less oxygen - ie. roughly the same density as air, but a pure CO2 ballon sinks like a stone!!

[Clanad]

Sabbatical brachiopod? Long time...

[jo90]

Thank you brachiopod for that enlighening (and very amusing) answer - I am still trying to retrieve the brussel sprout from under the cooker.

[mycats]

LMAO I'm more concerned about the Swedish Au Pair and that onion!

[brachiopod]

Cheers, Clanad. Yes, bit of a sabbatical. I tend to just have a quick lurk and occassional post session these days.

Decent science questions were getting fewer and further between, and I just ended up on late-night drunken rants against the "hang the paedophiles" and "kill all Muslims" threads - and feeling disappointed with myself in the morning for rising to it.

Still, the therapy is going well, and I am limiting myself to just a few peeps every week.....

[Clanad]

Well, your wit, enthusiasm and knowledge (especially of thing geologic) are certainly missed, brachiopod...