The dribbling of tea down the side of a teapot while pouring—known as this teapot effect—is a minor annoyance for regular tea drinkers. But for physicists around the world, it has posed a knotty theoretical problem spanning decades of research, garnering an Ig Nobel Prize along the way. We thought researchers had finally closed often the book on the mystery of the teapot effect in 2019, when Dutch physicists came up with a quantitative model to accurately predict the precise flow rate for how much (or how little) a teapot will dribble as it pours.
But apparently there was still more work to be done to fill the few holes in the theory, and physicists at the Vienna University of Technology (TU-Wien) and College College London took them on. The researchers say they’ve finally developed a complete theoretical description for the teapot effect that captures the complex interplay associated with inertial, viscous, and capillary forces that collectively serve to redirect the flow of liquid when certain conditions are met. Gravity, however, proved to be less relevant; all it does is determine your flow’s direction. That means you’d still get the teapot effect on the exact Moon, according to the authors, but not if you poured green tea on board the International Space Station.
The researchers presented their theoretical calculations within a paper published in the very September issue of the Journal of Fluid Mechanics. And now they have announced the results regarding experiments they conducted to test their theoretical model. Spoiler alert: the model passed with flying colors. And while it might seem to be a trivial conundrum, a insights gained could help us better control fluid flow inside, say, microfluidic devices.
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