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Why does hot water freeze faster than cold water?





It seems a simple enough question - yet it has baffled the best brains for at least 2,300 years.

Aristotle agonized over it fruitlessly in the fourth century BC

Roger Bacon in the 13th century used it to advocate the scientific method in his book Opus Majus

Another Bacon, Francis, wrote in his 1620 Novum Organum, that "slightly tepid water freezes more easily than that which is utterly cold" but could not explain why

Descartes was defeated by it in the 17th century AD

Even perplexed 20th and 21st century scientists and intellectuals have swarmed over it without result

Now the Royal Society of Chemistry is offering £1000 to the person or team producing the best and most creative explanation of the phenomenon, known today as The Mpemba Effect.

PLEASE NOTE: Handling hot or boiling water should be undertaken with care or under supervision.

Competition judges will be looking for an outside-the-box, inventive submission. In addition, the format of the submission should be creative and eye-catching.

Any medium or technology can be employed to make the case, including articles, illustrations or even film.

Submissions can be based on, and reference, existing research. The winning submission will be scientifically sound, and arresting in presentation and delivery.

The public has four weeks to crack the case before a group of the world's brightest young science brains take on the challenge in London as one aspect of a special science communications meeting entitled Hermes 2012.

Fittingly, that group's bid for glory will be made in the first week of the Olympics. The sharpest international postgraduate science students will travel to England from around the globe to participate in the Hermes 2012 event.

The Royal Society of Chemistry is sponsoring this visit to the UK of the hand-picked young scientists, who will gather at Cumberland Lodge in Windsor Great Park.

The organisers of Hermes 2012, based at Imperial College, chose the opening weekend of the Olympic Games for the academic event to underline the global nature of the meeting, with its temporary, multi-national community of high-achievers.

A highlight of the Windsor event will be a team attempt to produce videos to explain various scientific phenomena, which will include The Mpemba Effect.

"Why does hot water freeze faster than cold water?"

Royal Society of Chemistry President Professor David Phillips said today: "Modern scientists are still perplexed at this seemingly simple question.

"Ice cream makers and bartenders alike use the fact that hot water freezes more quickly than cold water every day in their work, but no one really knows why it works. The problem has been around for millennia, with philosophers such as Aristotle and Descartes pondering over it.

"But this effect was reintroduced into the scientific world in 1968 by Erasto Mpemba, a young inquisitive student in Tanzania during a lab session.

"Erasto questioned a teacher on why ice cream froze more quickly when it was boiled, and was quickly told that he was wrong and had probably imagined it. It was only when the teacher performed the experiment himself that he noticed this unusual phenomenon.

"Since the discovery of the effect, scientists have been trying to find out why the phenomenon occurs but remain divided as to what the answer is. It seems that there are lots of possible answers but a conclusive explanation hasn't been produced yet.

"The Hermes group members are, one might say, Olympians of the scientific world. The question is, can someone else out there give us an outstanding explanation before the postgraduate elite get down to their work?