Re: Money to burn?

["Daniel L. MacIsaac" <Dan.MacIsaac@NAU.EDU>]

> Condensation nuclei are required for cloud formation at saturation
> (really, just above saturation).  No argument there.
>
> Apparently, however, there is some disagreement as to whether there are
> sufficient cloud condensation nuclei in the jar BEFORE one adds the smoke.
> I would argue that even before you add some smoke to the air in the jar,
> the air in the jar has many, many condensation nuclei.  After all, do
> clouds only exist where smoke is present?
>
> Again, my concern about the demo is that it implies that "regular" air is
> devoid of condensation nuclei.
>
> ----------------------------------------------------------
> | Robert Cohen               Department of Physics       |

You might check out "Clouds in a Glass of Beer: Simple Experiments in
Atmospheric Physics" by Craig Bohren (should be <$20 from Amazon), which is
a delightful read on this sort of thing.  Bohren distinguishes heterogeneous
nucleation (where something else nucleates the cloud) from homogeneous
nucleation (where the molcules are cooled enough to "stick" in their collisions
and nucleate themselves.  You get heterogeneous nucleation on the insides
of the beer glass or from salt or sand (uck) particles in beer.  You get
homogeneous nucleation in the throat of the bottle when you uncap and
release pressure, dropping the temp to about -36C and making the cloud in
the neck of the bottle.  This is my fave cloud making demonstration :^).

Not sure if this is germane, but I love collecting physical fact about beer.
Making water hammers to knock bottle bottoms out and dissecting
Guinness cans for the widget etc is pretty entertaining research :^).

Dan M
(who just got thirsty)

Dan MacIsaac, Assistant Professor of Physics and Astronomy, Northern AZ Univ
danmac@nau.edu          http://purcell.phy.nau.edu         PHYS-L list owner