The secret of perfect stone grinding discovered by scientists

Competitors compete in the World Skimming Championships held on Easdale Island on September 25, 2016 in Easdale, Seil, Scotland (Getty Images)

Competitors compete in the World Skimming Championships held on Easdale Island on September 25, 2016 in Easdale, Seil, Scotland (Getty Images)

Heavier and more curved stones, rather than flat rocks, glide over the surface of the water more efficiently, according to a new study.

Skimming or “skipping” of rocks occurs after they collide at a low angle with a body of water and exit as they bounce off the water surface.

Experienced rock throwers know that the size and shape of rocks play a role in their ability to glide through the water.

Until now, it was widely believed that flat and round boulders were best suited for “jumping” stones over long distances, capable of bouncing off the surface of the water several times before sinking.

But a new study, published Wednesday in the journal Proceedings of the Royal Society Afound that larger and more rounded rocks produced the best results.

The researchers, including Ryan Palmer of the University of Bristol, developed a mathematical model to quantitatively predict how the shape and mass of an object influenced whether it was swept away.

They found a relationship between the mass of the stone and the curvature of its bottom to determine whether it could slip or not.

The study showed that heavier stones – which might otherwise sink – could slide on the right curve from below.

“The increased convex curvature of the landing gear implies an increased likelihood that degreasing will be successful,” the researchers wrote in the study, adding that the exact conditions at the entrance also play a role.

The researchers add that the study assumes “good technique” and that the speed and angle of throwing the stone also play a key role in whether it slips.

The findings suggest that a stone that is, for example, 8 times heavier than a successfully sliding pebble can still skip, provided its convex curvature is 4 times that of the pebble.

“The study, which looks at all smooth body shapes, basically shows that shape has a significant effect on the early and middle phases of a successful disguise, but is less significant during the final exit phase, when the body bounces off the water,” added the researchers.

Scientists believe the new findings also have applications in a variety of industries, including better understanding the bouncing of meteors on Earth and other celestial bodies, as well as landing airplanes in bodies of water.

The results also help shed better light on how ice builds up on planes with altitude and how this can be remedied.

“In this case, the skimmer is the ice crystal and the water is the layer on the plane. Aircraft icing is a fascinating topic that combines mathematics, physics and engineering, and is worth digging deep into,” said Dr Palmer.

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