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I was watching the bobsleigh event at the Winter Olympics and it was foggy. The commentator said that the extra humidity caused by the fog would 鈥渟tick to the track鈥� and slow the competitors down. How? I would assume extra moisture in the air would make the track more slippery and thus faster.

鈥� The essence of success in a bobsleigh competition is speed. Ice is laid down on the concrete course in millimetre layers over several days to a thickness of around 5 centimetres. The concrete is networked with plumbing, through which ammonia refrigerant flows, keeping the ice at about -6掳C. The ice meister, who oversees the track, uses sensors in and around it to keep informed about the conditions, so all aspects of the course are controlled and optimised for speed.

Nature is harder to manage, and humidity can pose a problem. If the temperature drops towards the dew point, moisture condenses from the air and a crystalline frost forms on the ice. This hoar frost acts as a brake under the sleighs鈥� runners. Before racing, the track is shaved and sprayed to ensure no frost or bumps remain to slow down the sleighs.

You can experience the unlikely friction caused by frost if you walk on an icy path in the evening, then again the next morning when there is a fresh covering of hoar frost. You will find that your grip is greatly improved.

David Muir, Edinburgh, UK

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This article appeared in print under the headline 鈥淪ticky ice鈥�