# Can we measure the curve in a glass of water?

The earth is curved, of course, and although the ocean looks perfectly flat, clearly it is not. It is curved. Slightly. Even 1/2 of an ocean is curved. Even Lake Michigan is curved. Even the surface of water in a drinking glass is curved. It seems that such a curve is virtually a straight line. We can calculate that curve, of course. Can we observe it? Can we measure it? How might we do this?

Surely it will be swamped by the meniscus induced by the sides of the glass, which is easily visible.

Where is this ocean that ocean

?

For a 3-inch wide glass of water, a little elementary geometry shows this bulge to be approximately one angstrom (10[sup]-10[/sup] metres.) This is pretty darn close to the size of a single water molecule, and at that scale it’s not really possible to view the surface of the water as continuous.

Thank you, MikeS, that’s the kind of idea I was looking for. **Janeslogin, **I don’t know about you, but when I look at the water, it looks flat in every direction. You can see the Earth’s curvature?

My guess is that Janeslogin meant that the ocean looks kinda… wavey.

One doesn’t even need to go to the ocean to see the earths curvature. http://historytogo.utah.gov/utah_chapters/the_land/bonnevillesaltflats.html
Here it is mentioned in the last paragraph.

ISTR in optics folks using pools of oil or mercury as optical “flat” surfaces for testing/reference purposes.

I also seem to recall that it was on the order of inches across before a “flat” liquid wasnt optically flat enough. So, a few inches would be a borderline case. With fancier optical methods I imagine you could measure it.

Far be it from me to argue with the august boyars of the fine state of Utah, but I doubt that very much. We recently had a thread on the topic and I think it was agreed that even the large expanse of water in a great lake or the ocean appears to be flat at the horizon and doesn’t appear to curve up or down from ground level.