Does that water seem too hot? It sure doesn't sound like it. Most people are quite good at distinguishing between the sound of a hot liquid and the sound of a cold one being poured, even if they don't realize it.

But research completed by Tanushree Agarwal, a psychologist at the University of California, San Diego, demonstrated that three-fourths of the participants in her experiments could in fact detect the difference.

In general, cold water sounds brighter and splashier, while hot water sounds duller and frothier. But until recently no one had evidence to explain the difference.

However, Xiaotian Bi, who earned a Ph.D from Tsinghua University in Beijing, offers a new explanation in a paper he and colleagues recently published. It's all about the size of the bubbles that form during pouring, he says.

PREVIOUS research showed that larger air bubbles in liquids produce lower-frequency sounds.

Dr. Bi also found that the acoustical spectrum of hot water has more low-frequency sounds than the spectrum of cold water.

He wondered, then, whether pouring hot water into a container would trap larger bubbles than pouring cold would, and whether that might explain the difference in sounds. His hunch proved correct. [ Sam Kean ]


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