Today's useless fact - Does hot water really freeze faster than cold water?

The phenomenon you describe is known as The Mpemba effect and is one of modern science's few remaining mysteries and the source of much debate in certain circles. Given the right set of conditions, hot or warm water can freeze faster than cooler water. This strange phenomenon was described by the likes of Aristotle, Bacon, and Descartes, yet is named after the Tanzanian high-school student who demonstrated it in 1969. The Mpemba effect only occurs under very specific sets of conditions and is still not completely understood.

Though the effect has been reproduced successfully in a number of experiments, no one can say with certainty why it happens due to the great number of variables involved. However, it is generally believed some combination of factors, such as evaporation, convection, conduction, and supercooling, may account for the Mpemba effect.

You'll be glad to know that however mysterious the phenomenon is, the Mpemba effect is put to good use by many ice-cream makers, who use warm milk instead of cool to help their ice cream freeze more quickly.

You may also be interested to know that for such a seemingly simple substance, water is surprisingly complex, and its behavior is poorly understood. The Mpemba effect is just one of 38 anomalies of water. Check out the links in our Water category for more.