# What stones are best for throwing “pancakes”?

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Scientists say that heavier, potato-shaped, rather than flat, stones will help you make the best throw.

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Researchers from the University of Bristol have studied different types of rocks that will allow you to make the farthest gliding jumps on the water, writes The Guardian.

Contrary to popular belief about the priority of thin and flat stones, the scientists' mathematical model shows that heavier stones, shaped like potatoes, can achieve better results. “Try some weird rocks and see what happens,” said Dr. Ryan Palmer, an applied mathematician at the University of Bristol. “Try throwing a stone shaped like a potato. With heavier stones, you can achieve funny things.”

Palmer and his colleague Frank Smith, a professor of applied mathematics, created a mathematical model to understand how shape and mass object affect the sliding on the surface of the water. In addition to more humorous applications, this model will help scientists work on commercial problems such as aircraft icing at altitude or the difficulties of landing aircraft on water.

With this model, the researchers were able to determine the mathematical relationship between the mass of a stone and the curvature of its underside, which determined whether it would slide or not. And they came to the conclusion that with sufficient curvature, heavier stones will glide much better.

But there is one caveat. Heavy stones, although they create a large tension on the surface of the water and bounce much further, they cannot produce frequent bounces, like smaller and flat ones. It turns out a kind of one-time “almighty” jump from the water.

According to the study, heavier stones with a curved base can bounce off the water because the curvature changes how the stone comes into contact with the water. At the first contact, it is pressed into the water deeper and longer. As a result, the pressure of the water on the bottom of the rock lasts longer and the surface of the water deforms more, both of which push the rock up.

“You're actually turning a horizontal throw into a more vertical movement. This results in an increase in the water's repulsive force, which helps to overcome the mass of the stone, and push it back,” Ryan added. “If the stone were flat, it would be difficult to slide.”

The model did not take into account the rotation of the stones, although previous studies have shown that this factor has a positive effect on throwing “pancakes”. The main effect is the stabilization of the stone due to gyroscopic forces while sliding in the air. If the stone is initially thrown correctly, the rotation will prevent it from turning in flight and hitting the water at the wrong angle.