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Earlier today, I came across a strange phenomenon involving a just-washed wine glass and a countertop. The gist of it is: when you place a warm wine glass upside-down on the wet countertop, it starts wiggling and sliding towards the edge.

I've repeated it several times, and found it only works when the glass was recently ran under hot water and it works best if there's already some water on the counter.

Because of the fact that it always moves in kind of the same direction, I'm guessing there is a slight incline on the countertop responsible for this. I'm trying to figure out exactly what is going on, since it's a pretty interesting thing that I've never seen before.

My current hypothesis is that the warm air inside the glass creates a pressure difference and a slight vacuum that pulls water under the lip of the glass, reducing friction to the point where gravity can pull it down. However, my friend thinks that the incline isn't enough for gravity to account for the speed at which the glass moves, and seeing that the speed is relatively constant (no observable acceleration) I'm thinking he might be right. Any thoughts or suggestions on further tests to find out what might be going on?

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