By William Derryberry, Kristopher Tierney for Spring 2014 Team Third.
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A sphere spinning in a shallow pool pumps water up along its surface due to the increase in tangential velocity with height. At the equator, the water is thrown off. Water thrown from a wet tennis ball forms spiral streams as each droplet starts out with the tangential velocity of the surface plus some radial velocity. Droplets that leave the same location on the sphere a bit later have rotated a bit further and start with a slightly rotated velocity vector, resulting in spiral streams.