FYFD

Tag: lubrication

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    Hot Spheres Sink Faster

    New research shows that the Leidenfrost effect–which causes water droplets to skitter across a hot pan–can drastically reduce the drag on objects moving through a liquid. When raised to a high enough temperature, a sphere falling water will be coated in a protective layer of vapor (see video above) that acts like a lubricant as the sphere moves through the water. If the temperature of the object drops too low, the vapor layer will dissolve into a mess of bubbles (~35 secs into video). One way that this mechanism reduces drag is by keeping flow attached to the sphere for longer as shown in this video. Preventing this flow separation increases the pressure recovered after the point of lowest pressure (the shoulders of the sphere), which reduces overall drag.

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  • The Roaming Rocks of Death Valley

    The Roaming Rocks of Death Valley

    The dry lake beds of Death Valley National Park in California are home to a perplexing phenomenon: roaming rocks. These rocks, some of which weigh hundreds of pounds, leave long furrows in the dirt but have no obvious means of propulsion. One theory posits that the rocks glide on collars of ice around their base. The ice acts like a flotation device when rain wets the valley and then the rocks slide so easily that high winds can move them across the surface. #