THE SECRET TO SLOSHING

CALL THIS a First World issue. A study has found that a glass of beer is less likely to spill than the same glass filled with coffee because bubbles cause friction that prevent it from sloshing. Just like a collection of tiny shock absorbers, liquid foam reduces movement by absorbing energy and the thicker the foam, the greater the effect – so if it’s a long walk from the bar to the table, a Guinness may be your best bet, physicists at Princeton University have found. Study lead Alban Sauret said: “You only need a few layers of bubbles to damp sloshing significantly. Once the foam thickness reaches a certain value, the damping is so strong that the surface of the liquid barely moves upon impact. So an impact that would make your coffee spill barely disturbs the surface of the beer. This is due to liquid friction when the bubbles rub against the walls of the container.” The physicists simulated walking with a drink in their hand and suddenly stopping by setting up a mechanical plate in a laboratory. They poured freshly brewed black coffee, Heineken and Guinness into three standard pint glasses until they were just over half full and placed them on the plate. Using a high-speed camera they recorded the wavy motion on the surface of the drinks. When the mechanical plate jerked, the coffee spilled over the rim of the glass, yet the Heineken and the Guinness stayed inside – with the Guinness sloshing the least. The scientists said that, as the waves form and travel, the foam rubs against the walls of the containers. This rubbing costs a lot of energy, which results in damping. The thicker the foam, the more energy is absorbed, and the less sloshing occurs. As well as solving a modern day conundrum, the researchers said their findings could be applied to industrial applications, such as the transport of liquid as cargo. All this just leaves one question – who thinks this stuff up and who pays for these studies?