[galpinj]

Hey guys!

So I was reading about surface tension on wikipedia yesterday. I read that in order to reduce the number of water molecules that are partially/fully unbound with other water molecules, water will create its own internal pressure (cohesion). This is particularly true when water is on a substance with poor adhesion. I think I understand why water will curve in a glass or become spherical droplets (maximize cohesion/# of particles surrounded by water molecules). My question, which may seem stupid, is why doesn't this kind of thing happen in larger bodies of water, like a lake or pond? Wouldn't there be more cohesion if the water was curved? If this isn't the case, then why does water curve when you have a droplet?

Might be a dumb question, but I haven't been able to figure it out; thanks everyone!

[Burner]

Theoretically water surface will still become curved due to surface tension in large water bodies, but we seldom be aware of them. Also, the soil in lakes or ponds may allow water molecules to adhere to better.

[galpinj]

Hey man, thanks for the reply.

What about when we just look at an example of pure water. The molecules on the surface have strong intermolecular forces with those water molecules beside and below, but nothing above. Wouldn't this create a net force DOWN, thus creating a concave-like surface??

https://www.google.com.tw/imgres?imgurl=http%3A%2F%2Fbutane.chem.uiuc.edu%2Fpshapley%2FEnlist%2FLabs%2FSurfaceTen%2F6.png&imgrefurl=http%3A%2F%2Fbutane.chem.uiuc.edu%2Fpshapley%2FEnlist%2FLabs%2FSurfaceTen%2FSurface.html&docid=kJMzE78JE3wO9M&tbnid=dbqGeP6UysTGkM%3A&w=604&h=374&hl=zh-tw&client=safari&bih=672&biw=1024&ved=0ahUKEwj3-_yZ4JLNAhVL3GMKHfslDr4QMwgoKA4wDg&iact=mrc&uact=8

[Borek]

All those effects are visible only close to the edge - surface is curved just a millimeter or two from the place where water touches something else. That's because other forces involved are much stronger.

[Enthalpy]

It does create a net force on the surface molecules towards the depth of the liquid. This is the proper way to understand surface tension, better than the complicated explanations given so often. At the surface of a lake, depth means downwards, yes again.

Since the superficial molecules at North or West also get the same force, this alone doesn't curve the surface. The surface deeper at one location implies that it's higher elsewhere, negating any gain. So on a big surface, you won't notice a significant curvature.

Things change at the ends of the surface. There, it depends on how strongly the container's surface attracts water molecules: more or less than the water molecules attract an other. If the container attracts more, water climbs a little bit against the container; if not, water joins the container lower.

This effect can compete against gravity in the mm scale. Since the energy of surface tension increases as an area but gravity as a mass hence volume, at a bigger scale gravity wins. So surface tension is all-important for fog droplets and mosquitoes, but negligible for the shape of a lake.

Surface tension is more effective if the contact area increases as compared with the volume. This is the case in a capillary tube or at a wick, where capillarity can raise a liquid higher.

[mikasaur]

The problem is that surface tension is only so strong, and the gravity of the earth is competing against it.

Think of a giant spherical water balloon filled with water. The balloon itself is kind of like surface tension; it wants to keep a spherical shape and applies forces through the "surface" of the water (where the balloon meets the water).

In outer space, the balloon would remain completely spherical because the forces involved allow it to be that way. There's no earth to apply gravity to it.

Now imagine our balloon sitting on the surface of the earth. The shape isn't spherical anymore... not at all! It flattens out a lot.

The "surface tension-like" effects of the balloon are stronger than actual surface tension effects in water, so water without a balloon flattens out even more so than a balloon would.

It's not a perfect analogy but I hope that helps.

[Arkcon]

I think I understand why water will curve in a glass or become spherical droplets (maximize cohesion/# of particles surrounded by water molecules).

See, your initial premise was flawed, and it lead you far and away to a false conclusion.  Water definitely doesn't show cohesion on glass, that's mercury.  Water definitely adheres to other things except hydrophobic things, so the ground surrounding a pond or a lake has no problem attracting water. m In addition to what was mentioned above.