Why Water Expands When It Cools


Water droplet

Most of us, when we take our first science classes, learn that when things cool down, they shrink. (When they heat up, we learn, they usually expand.) However, water seems to be the exception to the rule. Instead of shrinking as it cools, this common liquid actually expands. In order to explain this phenomenon, some scientists have adopted the “mixture” model, which purports that low-density, ice-like components dominate due to cooling. Masakazu Matsumoto, at the Nagoya University Research Center for Materials Science in Japan, has a different idea. He describes his findings in Physical Review Letters: “Why Does Water Expand When It Cools?”


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