SKATERS know how slippery melting ice can be. It turns out that ice also reduces friction under water.
Ivan Vakarelski of the King Abdullah University of Science and Technology in Thuwal, Saudi Arabia, and his team made ice-coated tungsten carbide balls to match the size and weight of solid steel balls. They then dropped both kinds into a tank of water to see which fell fastest. 鈥淚f you think about the physics, it鈥檚 not obvious what the answer is,鈥� says Derek Chan of the University of Melbourne, Australia.
The icy balls fell faster and had far less drag. High-speed video showed that when the balls first entered the tank, a turbulent wake formed behind them, slowing them down. But as they fell, their wakes narrowed, streamlining their path through the water. Icy balls dropped in 22 掳C water reached that point much faster but did not get a speed boost in 6 掳C water, where they melted less (Physical Review Letters, ). This suggests that melting ice is key 鈥� it may transfer momentum away from the ball鈥檚 surface. The discovery could help with studying icebergs, says Chan.
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This article appeared in print under the headline 鈥淚cy balls fall faster than steel in water鈥�
