Sidewalk Science: How Water Splashes Atop Your Shoes

Walking on a wet sidewalk after a rainstorm leaves the tops of shoes soaked, according to calculations presented at last week's meeting of the American Physical Society in Pittsburgh.

A team of researchers who usually work on nanoparticles and lasers studied the phenomena to figure out how to avoid getting their socks wet during their lunch hour strolls.

Jake Fontana of Ohio's Kent State University coated a floor with a thin layer of water and set up a high speed camera to record his walk. The camera revealed that when his shoe makes contact with the wet ground, it lifts a wedge of water up with the heel. The liquid slides forward along the bottom of the shoe as the foot swings forward, and is kicked into the air at the top the shoe's arc. The water shoots off at the precise angle – 75 degrees – that causes it to splash onto the tip of the shoe as the foot comes down for another step.

The small numbers of drops released by each step add up – walking half a mile dumps the equivalent of a pint of liquid on the shoe top.

"One solution would be to make shoes like car tires, with treads that push water out and away from the direction of the step," says Fontana. A simpler solution, he says, is to walk a little slower to change the fluid dynamics involved.

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Inside Science News Service is supported by the American Institute of Physics.