Heavy stones can skip water, physicists say, too: NPR

Flat, light rocks like the one pictured above are preferred for skipping stones. A new study found that heavier rocks can skim the surface of the water, too.

Jeff G Mitchell/Getty Images

Hide caption

Switch caption

Jeff G Mitchell/Getty Images

Flat, light rocks like the one pictured above are preferred for skipping stones. A new study found that heavier rocks can skim the surface of the water, too.

Jeff G Mitchell/Getty Images

When skipping a stone through the water, most people look for flat, light stones. Now, a new study suggests that heavy, curved stones can also lead to impressive slips. Not only will these findings help you improve your game, they can be applied to the real world, such as helping make planes more efficient.

Ryan Palmer is an applied mathematician at the University of Bristol in the UK and co-author of the study, Posted this month in the Royal Society.

He and his colleagues created a model to see how shape and mass affect the way organisms interact with water. And they found that when skipping rocks over a lake, “if you pick something a little heavier, you get something called a hyperelastic response,” Palmer said.

In other words, a heavier body It can yield an impressive bounce.

“What happens is that the rock touches the water layer, and because it’s heavier, it sinks further and stays in contact longer,” Palmer said. “This increases the pressure on that rock, which then increases the force that lifts it, and you can get a strong jump in that response.”

Now, Palmer admitted that while you might get a big jump with heavier stones, it won’t result in as many skips as with flat stones. Results also depend on the shape of the stone, as too heavy a type may not work.

“So taking it home is really, for a heavier rock that might sink, if it were a little bit more bent, it might be more likely to go down,” he said.

Palmer and his colleague were studying more than the physics of skipping stones. With the mathematical model, they sought to better understand aircraft icing, a phenomenon that occurs when planes fly in very cold weather.

Sometimes, puddles of water form on the wing of an aircraft, and ice crystals can come into the air and sink into or descend from that puddle. If it sinks, it leads to ice buildup that can be dangerous.

But if they skim, Palmer said, “Well, it’s the same physics and dynamics that you would find if you picked up a rock and tried to throw it across a lake.”

Palmer said it’s important to know where the ice might go in order to understand if other parts of the plane need more protection.

He also insisted that commercial aircraft were safe; Systems are in place to protect them from dangerous ice build-up. His research aims to increase the efficiency of that protection.

“As we live in this world of climate change and increased fuel costs and stuff, you’re always striving to be more efficient, so you can design your systems better, better protect aircraft,” he said. “You can cover these strange situations that may occur in an effective and innovative way.”

And while Palmer sought practical applications, that wasn’t the only thing he took away from his research.

“Since starting this business, it’s become very difficult to try to peel the stones, and especially kind of pick the ones that are a little bit more exotic,” he said. “The ones that aren’t necessarily very flat.”