Skimming stones

Mathematicians at University College London have drawn up an equation that works out how to play the childhood pastime of stone skimming or "ducks and drakes".
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The model compares the weight and speed of the stone with air and water resistance and gravity to come up the perfect throw.
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While the research was carried for fun it also has a serious side as it can be used to calculate the behaviour of ships in rough seas and ice skipping over aircraft wings and fuselages.
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Professor Frank Smith, an applied mathematician carried out the work with his colleague Dr Peter Hicks.
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He said that there was no reason why up to 50 "bounces" was possible, according to the formula.
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Theoretically it is possible to reach around 50 but I admit the most I have achieved is eight.
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He said that the key to a good throw is to spin the stone, to maintain stability.
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Pick a stone which is as thin and light as possible
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Throw it with as much force as possible and as horizontal as possible and from as low to the ground as you can.
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Spinning it in the air helps it fly and reduces the air resistance.
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That should get you the maximum amount of bounces.
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The record number of skims is 51 held by Russell Byars, an American engineer, who achieved the feat on the Alleghany River in Pittsburgh.
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He recommends that you pick flat palm sized stones and use your thumb and forefinger to spin it.
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Aim to hit the water at between 10 to 20 degrees, he adds.
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The texture of the pebble surface is important too but experts are divided over what is best.
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Some say that the stone needs to be as smooth as possible in order to skip unencumbered across the water.
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Others, like French physicist Lyderic Bocquet of Lyons University, says lots of small pits on the stone surface will reduce water drag in the same way that the dimpling on a golf ball reduces air drag.
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Next time you are next to some water see what you can do