Shaking a drink in a martini glass creates mesmerising patterns of small whirlpools.
at the University of Waterloo, Canada, was travelling abroad when he ordered a drink in a bar and stumbled upon an intriguing physics discovery. His martini was full of bubbles, and because he was sitting by a window, he could clearly see them trace a complicated structure of vortices when he shook the glass back and forth.
Later, he repeated the process in the lab with a mixture of water, glycerine and food dye instead of a cocktail and discovered that the phenomenon was reliably repeatable. Pan and his students then tried shaking a range of mixtures, each with a different 鈥淩eynolds number鈥� 鈥� a measure of the imbalance between particles in a fluid being propelled by inertia and getting slowed down by viscosity.
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For mixtures with a high Reynolds number 鈥� which anyone can achieve by adding lots of syrup to a drink 鈥� shaking the martini glass produced a pattern of vortices that resembled elongated hearts when looking into the glass from above. When the researchers shook liquids with very low Reynolds numbers 鈥� meaning they were less viscous 鈥� four symmetrical vortices emerged, producing an effect like a four-leaf clover with a small whirlpool at each petal鈥檚 centre.
鈥淭he first thing that occurred to me when I saw this is that anything that can have a specific pattern must have some theory behind it, there might be a nice combination of physics and maths in this beautiful problem,鈥� says , also at the University of Waterloo, who collaborated with Pan on a series of stunning photographs of the new phenomenon, which will be presented at the in Washington DC later this month.
Pan says that while his team does not have a good mathematical understanding of this effect yet, one related system is how fluids slosh in moving containers 鈥� like the fuel in a ship鈥檚 fuel tanks. Such fluids have been studied before, but researchers had focused on the rise and fall of the liquid while the vortices went unnoticed. Strikingly, the flow patterns inside a shaken martini glass also relate to rip currents seen in coastal areas, as in both cases fluid hits an inclined edge, be it glass or a sandy shore, and reflects off it in a strong jet outward, says Pan.
