Caitlin Stier, video intern
It's not just flat stones that can skip across the surface of water. Despite their spherical shape, water-bouncing balls can jump across ponds just as seamlessly.
Now Tadd Truscott and his team at Brigham Young University in Utah are revealing how the design of these balls allows them to accomplish the feat. To conduct tests, they headed to a nearby pond armed with three types of balls. Then they hurled them into the water as cameras filmed the action above the surface and a naval tank captured motion underwater. Their footage highlights the forces that make the different balls sink or skip.
In terms of water skimming, the superball faired the worst. Despite its springy action on solid ground, its high density and low surface area caused it to plummet in water. The racquetball displayed some bounce due to slight flattening on impact but this short-lived shape only propelled it for a few leaps.
The water-bouncing ball, however, was able to maintain a crushed shape for longer to help it scoot across the pond. Its contact area with the water increased when it was squished, helping it to ride along. The ball sprung from the water over 20 times, covering a stretch of nearly 60 meters.
Truscott first became interested in water-bouncing balls after his nephew introduced him to their abilities over the summer. For his next project, he plans to investigate the rolling effect that occurs near the end of a series of leaps across the surface.
The group presented their findings this week at the American Physical Society's fluid dynamics meeting.
If you enjoyed this video, see how a ball could sink forever in a sea of sand-like material or check out this ball-catching robot.
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