Tuesday, May 19, 2015

Does hot water freeze faster than cold?

In some circumstances, it does. The question is a old one, dating back at least to Aristotle, and turns out to be surprisingly complex. This paper is a good study in the subtleties of getting clear answers from Nature.
Monwhea Jeng
Physics Department, Box 1654, Southern Illinois University Edwardsville, Edwardsville, IL, 62025 
We review the Mpemba effect, where intially hot water freezes faster than initially cold water. While the effect appears impossible at first sight, it has been seen in numerous experiments, was reported on by Aristotle, Francis Bacon, and Descartes, and has been well-known as folklore around the world. It has a rich and fascinating history, which culminates in the dramatic story of the secondary school student, Erasto Mpemba, who reintroduced the effect to the twentieth century scientific community. The phenomenon, while simple to describe, is deceptively complex, and illustrates numerous important issues about the scientific method: the role of skepticism in scientific inquiry, the influence of theory on experiment and observation, the need for precision in the statement of a scientific hypothesis, and the nature of falsifiability. We survey proposed theoretical mechanisms for the Mpemba effect, and the results of modern experiments on the phenomenon. Studies of the observation that hot water pipes are more likely to burst than cold water pipes are also described.
H/t Faculty of Language.

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