Thursday, March 22, 2012
Ah, The Old Water Circling the Drain Myth
OK, it looks good. The trick is you have to start on the equator with a tube of still water, no motion. When you pull the plug it goes straight down. When he pours the water back in, above and below the equator, he imparts a spin to the water in the basin. It would be hard not to, but by choosing which way to pour the water in, he controls the direction of the spin, clockwise in the north and counterclockwise in the south. When he pulls the plug here, the spin in the water tries to conserve itself, and ends up being concentrated as a vortex at the end.
Coriolis "force" would try to impart such a spin, but it is so small, especially that close to the equator, as to be negligible. But it's a nice trick. I hope he got lots of tips, or at least a cut from the cut purses working the crowd.