From: utzoo!decvax!duke!harpo!seismo!rocheste!FtG
Newsgroups: net.physics
Title: physics of teabags
Article-I.D.: rocheste.319
Posted: Wed Dec 15 08:18:47 1982
Received: Sat Dec 18 21:24:55 1982

I've always enjoyed puzzling over the mysteries of everyday phenomenon
and I am usually successful in figuring out what is going on, but
I recently noticed something that has me stumped. Perhaps someone
out there in netland can solve this one.

When boiling water is poured over teabags, the bag very quickly
fills up with air. I found this annoying since I think it interferes
with the brewing. I can suggest four causes, but I am not satisfied
with any of them. There are listed below in the order of almost
plausible to the far fetched.

1. Thermal expansion of latent air in the bag. It appears that
the amount of air at least triples, but the coefficient of expansion
of air is less than .004/Degree C., which can only account for
an expansion by about 1/3.

2. Formation of water vapour, the tea leaves being great nucleating sites.
There are several problems with this- a) Not that much vapor should form
at the temperatures one expects in the cup shortly after pouring (the water
cools down very quickly), b) The vapour should recondense quickly when
the bag bobs to the surface.

3. Agitation- the act of pouring the water in stirs up the bag quite a
bit, but how this causes so much air to be "pumped in" is beyond me.

4. Volatile oils in the tea. The herbal teas I drink contain lots of
volatile oils which might form a nice vapour inside the bag when
heated, but I don't think it could possibly account for all of the
swelling. Comparing regular teas to herbal teas may be useful.

5. Its God's will. (Included to give Creationists equal time :-) )

Mail your ideas and arguments to me and I'll post back to the
net the best solutions if interest warrants.
Does anybody else out there have a favorite phenomenon they can't
explain?
			rocheste!FtG