…A team led by Stéphane Dorbolo from the University of Liége in Belgium decided to get to the bottom of these crazy things once and for all.Using some cameras, a nickel bead, a magnet, and Petri dish popsicles, the researchers simulated what happens when a sheet of ice floating on water starts to melt, as it would on a frozen river as the weather warms up.
Strangely enough, the ice sheet started rotating, even though the team hadn’t added any eddies to the model. Turns out, the spinning is actually down to some crazy properties in the water itself – not the currents it forms in a flowing river.
As Ryan F. Mandelbaum explains for Gizmodo, water happens to be at its densest at exactly 39.2 degrees Fahrenheit (4 degrees Celsius) – and that’s important. “In their experiments, the scientists measured the flow of the water beneath the ice, and found that the icy disc cooled the water surrounding it,” says Mandelbaum. “When surrounding water hit the 39.2 degrees point, it sank and formed a vortex. This vortex of water whirls the ice floating atop it.”
But while the paper, published in Physical Review E last April, finally explains the spinning, it doesn’t explain how the disc ends up in such a perfectly round shape. It could be that shards of ice are collected up by the vortex and added to the disc to form the circle shape, or maybe the circle shape develops gradually – the disc smoothes itself out over hundreds and thousands of rotations. Edited from:– ScienceAlert