This metal ball may not look like hot stuff, but it can travel through water in a flash. When hot objects move quickly through a fluid, they exhibit something known as the Leidenfrost effect, where cavities of air form around them. Scientists wanted to use this property to decrease friction and drag as much as possible. Unlike previous research, where balls were passed through liquid inside a small bubble, the researchers aimed to make the largest cavity they could. By heating some balls to absurdly high temperatures—400oC—and dropping them into 90oC water, the 20-millimeter-diameter balls were encapsulated by a tear-shaped cavity that was five to 15 times their size, which cut through the water like a hot knife through butter. In other trials, balls were coated in a material that repelled water, which generated a similar cavity without the need for the high temperatures. When the balls were raced against a similarly weighted tear-shaped piece of plastic, the treated metal balls had 90% less drag, the team reports today in Science Advances. The researchers say that this “cavitation” could help decrease drag in watercraft. And with the reduction to that major obstacle, speeds and fuel efficiency would sharply increase.
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