Re: What is the maximum size for a drop of water?


John Wilkins wrote:
Nic <harrisondalen@xxxxxxxxxxx> wrote:

Manny Feld wrote:
r norman wrote:


The problem, as has already been mentioned, is the drop breaking up by
wind shearing forces as it falls through air. I seem to recall
astronauts playing with enormous globules of water floating in zero
gravity. Surface tension holds it together, but is a rather weak
force especially as the surface area grows more slowly with drop size
than the inertial or gravitational disruptive forces on the mass.

In free fall one can assemble some rather large water drop.

But there still must be a limit. Water isn't very dense, so it would
be interesting to know whether in the case of a very large drop, the
event horizon would be below the surface.

Surely it would be at the point where (on average) the stresses of
internal thermal agitation and prior kinetic energy imparted to the
water exceeded the cohesion provided by surface tension? Assuming that
there are no internal stresses at the limit, and the water needs to be
at least 0°C, how big could a stable drop get? I guess that you have to
factor out tidal stresses too in microgravity.

I was talking about seriously large drops here. I imagine the
significance of surface tension vanishes as size increases. It would
be superseded by own gravity. Either mechanism gives rise to a
spherical shape. (For this I was assuming the drop is in an
environment such that there is an adequate partial vapour pressure of
water to prevent a rapid loss due to evaporation, so we don't have to
worry about icing over or boiling.)

For more moderately sized drops, and I think this is your point, could
Brownian motion break them up if they are so large that surface tension
can be ignored, but still too small for own gravity to be significant?

I doubt it. But who knows?

--
John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project
University of Queensland - Blog: scienceblogs.com/evolvingthoughts
"He used... sarcasm. He knew all the tricks, dramatic irony, metaphor,
bathos, puns, parody, litotes and... satire. He was vicious."


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