A Mystery in a Teapot
Krystal Slagle/iStockphoto/Thinkstock

Read our COVID-19 research and news.

ScienceShot: A Mystery in a Teapot

For centuries, physicists have made their living by illuminating the secrets of our universe, from gravity to electricity to black holes. But among the search for Higgs bosons and the endless unspooling of string theories, there remained a particularly glaring mystery: Why does a teakettle whistle? “Oh that,” they said, standing at their stoves in between bouts of programming supercomputers. “Vibrations. Or something.” Now, we are happy to report, human intellect has at last triumphed over the dark shadow of ignorance and solved the conundrum lurking within one of our lowest-tech kitchen appliances. After years ensconced in the ivory tower of the University of Cambridge in in the United Kingdom, a team of researchers has emerged with an accurate mathematical model of a teakettle’s whistle. It has not one but two phases, they tell us. The first begins as the steam is forced into a jet by the kettle’s narrow spout; as the rushing air is compressed and then escapes into your kitchen, it vibrates with the frequency of a welcoming whistle. But the water inside the kettle is still boiling, sending more and more steam through the spout at faster and faster speeds. When the flow speed passes a certain point, tiny whirlpools form in the steam and radiate sound waves that eventually overtake the original vibrations. The new model is so accurate that physicists can now predict the pitch of any kettle’s whistle. And having solved another mystery of our vast but perhaps ultimately knowable universe, they smile and sip their tea.

See more ScienceShots.