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Physical Reasoning

A Failure of Common Sense: Cooling water to room temperature

In connection with Ernie Davis's 'Absolute Zero' problem, here's an experiment with a very counter-intuitive outcome. The apparatus is two containers, with one fitting loosely into the other. Hot water is placed into the inner one, and iced water into the outer one, forming a cooling jacket. The experiment measures how long it takes for the water in the inner container to cool to room temperature. If the initial temperature of the hot (inner) water is very high, it cools to room temperature in less time than if its initial temperature is lower.

Why is this surprising? More difficult, and maybe outside 'common sense,' what explanation could be given for it?

Contributed by Pat Hayes (, Institute for the Interdisciplinary Study of Human and Machine Cognition, University of West Florida, U.S.A. (19th September 1997)

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