Etsy Journal

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The Teapot Effect: Why Teapots Drip

by Karen Brown

Jan 2, 2013

What sparks the curiosity of a man who has attended lectures with Einstein and partied at Heisenberg’s house? Teapots.

Joseph B. Keller is an immensely distinguished scientist. Professor Emeritus in engineering and mathematics at Stanford University, he may be known best for the Geometrical Theory of Diffraction and the Einstein–Brillouin–Keller method. But his major work – honored with awards that include the National Medal of Science and the Wolf Prize – might not fully convey Dr. Keller’s sense of playful enthusiasm and perpetual curiosity.
What sparks the curiosity of a man who has attended lectures with Einstein and partied at Heisenberg’s house? For one, Joseph Keller is into teapots. Really into teapots. In fact, he is the world’s recognized expert on why teapots drip. Like many of us, Dr. Keller had long observed the pesky problem of that little bit of tea that always seems to run down the outside of the spout and drip into our laps. “Then, in 1956, I heard a lecture,” he told me. “An Israeli scientist reported he asked 100 physicists why teapots drip and they all said it was due to surface tension. This scientist did some experiments that proved it couldn’t be caused by surface tension, so what is the explanation? I wrote a paper, ‘The Teapot Effect,' shortly thereafter, showing that the effect occurred through fluid and mechanical forces.”
Dr. Keller showed that it was air pressure, not surface tension – that causes drips. “It is simply that at the pouring lip the pressure in the liquid is lower than the pressure in the surrounding air,” he said, “so air pressure pushes the tea against the lip and against the outside of the spout.” In 1999, he and his colleague Jean-Marc Vanden-Broeck described the final act in the drippy teapot scenario when they calculated where gravity makes the drop fall off the pot. For this, Keller won his first Ig Nobel Prize Award from Harvard, which celebrates the unusual and imaginative in science. (His second Ig Nobel Prize was awarded in 2012 for calculating why a jogger’s pony tail swings side-to-side while her head is moving up and down.)
Can Dr. Keller look at a collection of teapots and make a reasonable guess at which are more or less drippy? “Yes, I believe I can,” he said. He told me there are three things that help make a spout drip-proof. “The first thing is this,” he said. “If the teapot spout points up and then straight down at the pouring end, then the tea will flow back into the pot when the pot is turned upright again and a drip would be almost impossible.”
“Number two is this,” he said. “If the lower lip of the spout is sharp, as is the case with metallic teapots, then the trouble is ameliorated. The sharp edge would help prevent the tea from turning the corner. It’s still possible to drip but less likely if the tea is coming with any force. There are little metallic tools with sharp edges that fit over the end of a teapot spout that can covert a bad spout to a good one.” His third piece of advice for avoiding drips is not to have the teapot too full. “Tea from a less full pot will flow with greater velocity. The faster the flow, the less likely it is that the tea will cling to the lip.” [etsy_slideshow] Fundamental forces in our universe make teapots drip, the same forces that make life itself possible. So if we found ourselves in a universe where no teapots ever dripped, is it possible we might not be able to survive there to enjoy the tea? Dr. Keller chuckled at that idea. “The best I can tell you," he said with full scientific rigor, “is maybe.”
Karen Brown

Karen Brown is an award-winning designer and creative director of the Center for Ecoliteracy. Her work has been included in the Smithsonian Institution and Cooper-Hewitt National Design Museum, and featured in The New York Times, Architectural Digest, House Beautiful, and on Today on NBC. She believes that the handmade movement is a fundamental force for transforming society and the economy.