Potato-shaped stones are better for skimming, say experts

When skimmed across the surface, certain types of stone can leap out of the water.

The researchers found that heavier, potato-shaped stones can achieve more dramatic results than thin, flat stones.

Ryan Palmer is an applied mathematician at the University of Bristol. Throw a stone that resembles a potato. You can have fun with heavy stones.

The mathematical model was created by Palmer and Frank Smith, professors of applied mathematics at University College London. The model will help scientists work on more commercial problems, such as the build up of ice on aircraft at altitude, and the forces at play when planes land on water.

The researchers used the model to identify a relationship between the mass of the stone and the curve of its underside. They conclude that heavier stones will skim if the curve is sufficient.

If thrown well, bulkier stones can be thrown across the water a number of times, but not before they disappear beneath the surface. The curved stones interact with the water in different ways.

If you have a heavier rock, you can get a super-elastic response, where you get a single mega-bounce. There is a huge leap out of the water.

The game is changed by it. If you can do it, it's very satisfying.

Heavy stones that have a curved base can bounce off the water. It presses into the water for a longer time after contact.

The throw is turning into more vertical motion. Ryan said that an increase in the force of the water pushing back on the rock could drive the stone back out. The stone is too heavy to skim.

The model didn't look at the impact of spinning the stones, but previous research shows that spin is an important part of stone skimming. As the stone glides through the air, gyroscopic forces are used to keep it stable. The spin on the stone can stop it from hitting the water at a bad angle if it is thrown well.