| MadSci Network: Physics |
OK, this is one of those science tricks. The problem is simple - the meniscus of a water-air interface, that is, the surface of the water, in a vessel is usually concave; that is, it curves up at the edges.
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|\ <- meniscus ______/|
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| ---------------------|Cork| |
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| water in a container |
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So anything that floats will eventually slide to an edge, trying to float as high
as possible. How do we get it to float in the middle? I'll ask it a different
way first - how do we make the surface curve up in the middle instead of
at the edge? Think about it for a minute; if you can't figure it out,
continue reading.
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|/ \|
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| water in a container |
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Still stuck? OK, put the cork in the dish of water. Now, very
carefully, keep adding water to the dish (or bowl or glass or whatever)
until it is actually slightly more than full. The tricky part is getting
it overfilled without going so far that the water runs out, and it's
easier with a small area like a glass than a large area like a dish. If
you do it carefully, you can get the water to form a convex surface; that
is, one that curves down at the edges. And voila! the cork will float to
the center, which is now the highest point of the water!
Try the links in the MadSci Library for more information on Physics.