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Heavier, curvy stones can give surprising results in skipping, physicists say


Skipping a stone across water requires skill and patience and, of course, a great stone.


Personal preference here for a flat, light one, seems to skip easier. But scientists have found that is not the only way to get impressive leaps.

RYAN PALMER: If you pick something that's slightly heavier, you get something called a super elastic response. And so you throw it in, and you get this really surprising, big leap out of the water. Unfortunately, you're not going to get many skims, but you do get one big, impressive one.

SUMMERS: Ryan Palmer is an applied mathematician at the University of Bristol in the U.K. He and a colleague modelled how shape and mass affect the way objects interact with water. And they found that a heavier rock with a good curve - imagine the shape of a mango but smaller - they say that shape can get an impressive bounce.

PALMER: The rock touches down on the water layer, and because it's heavy, it sinks down further and stays in contact for longer. This increases pressure on that rock, which then increases the force that lifts it out. And you can get an almighty leap in this response.

DAVID HU: I just love it that people are still curious about skipping stones. I think it just gives me faith in science.

KELLY: David Hu is a mechanical engineer at Georgia Tech. He was not involved in the work. He says he is surprised the researchers studied curved objects.

HU: I think a lot of the attention on skipping has been trying to get the most skips. So there's this world record of 88 skips. But this study shows that if you use rocks that don't seem very skippable, you can get surprising things happening.

SUMMERS: The work was published this week by the Royal Society, and Ryan Palmer insists it does have real-world applications, like when airplanes fly through clouds, for instance.

PALMER: What happens is you get a sort of a puddle form on a wing, and then an ice crystal will come along and potentially skim off of that puddle on an aircraft wing. Well, it's very much the same physics and dynamics that you might find if you pick up a rock and you try and throw it across a lake.

KELLY: Ice buildup on planes can be dangerous and diminish performance. And though we already have systems to protect planes from ice, Palmer says this work is about making those systems more efficient.

PALMER: And so where we live in this world of climate change and sort of increasing fuel costs and things, actually we're always seeking to be more efficient. And so you can better design your systems, better protect planes.

KELLY: Which is not to say that practical applications are the only interest here for Palmer.

PALMER: I think since starting on this work, it's become even more irresistible to try and skim stones and particularly just sort of picking the slightly weirder stones, so picking ones that aren't necessarily so flat.

SUMMERS: And that is an experiment that anyone can try at home.


BOB DYLAN: (Singing) Like a complete unknown... Transcript provided by NPR, Copyright NPR.

Alejandra Marquez Janse is a producer for NPR's evening news program All Things Considered. She was part of a team that traveled to Uvalde, Texas, months after the mass shooting at Robb Elementary to cover its impact on the community. She also helped script and produce NPR's first bilingual special coverage of the State of the Union – broadcast in Spanish and English.
Christopher Intagliata is an editor at All Things Considered, where he writes news and edits interviews with politicians, musicians, restaurant owners, scientists and many of the other voices heard on the air.