"Eddie Munster" wrote in message
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MW is correct.




Michael Williams wrote:

Hmmm. I don't think you have this quite right. According to your
description, why wouldn't the water just be forced out of the gap?

I'm not getting this right, I don't think but if you are asking why water
between the two sheets of glass doesn't just run out, here's why:

Three reasons are most important.

First, the intermolecular attraction between the positive hydrogen atoms in
the polar water molecules and the negative oxygen atoms in the polar silicon
dioxide molecules of the glass is greater than that between the water
molecules themselves. This results in the "wetting" of the glass and the
disappearance of the water's surface. The interaction keeps the water in
place on the glass.

Second, there is air pressure at the edges of the glass pushing against the
very thin water surface that occurs between the pieces of glass. Since the
pressure is the same all around the resultant is a force pushing the water
towards the center of the glass. It doesn't go there because of the
considerations of "wetting" (as discussed above) pulling the water and
forcing its dispersal over all the glass surfaces.

Third, there is also a thin surface of water at the edges of the water
lamina forming a concave meniscus. This is the only place where surface
tension exists in the system because it's the only water surface, there
being no water surface inside the lamina. This is also a result of the
first reason above.

Agkistrodon