A coffee on the way to work is meant to inject a bit of energy into the morning, not end up a miserable puddle all over your lap. A team of scientists has now discovered that the best way to avoid this hassle is to order a latte, as the froth reduces the chance of the drink sloshing over the edge of the cup.
Study co-author Emilie Dressaire, a mechanical engineer at New York University, was made aware of the effect when she was told by a barista that a lid wouldn’t be necessary on her takeaway latte, as it was fairly unlikely to spill. A further connection came from the observation by her colleagues that Guinness, with its unusually large head, was much easier to carry from the bar without spilling than other, lighter beers.
Using water, glycerol and dishwasher liquid, fluids with various depths of foam on the top were created in the lab. These were then subjected to jolting akin to travelling on a bus, or walking, and high speed cameras recorded the waves produced on the surface of the liquid, measuring their height and speed of creation.
It was found that just 5 layers of tiny bubbles was enough to reduce the size of these waves tenfold, an effect attributed to foam at the edges of the cup helping to dissipate the sloshing liquid’s energy through friction. Any more bubbles made no difference, as the top layers didn’t really move much.
Although this may revolutionise commuters’ morning drinking habits, it also has more ambitious potential applications with regard to the transport of fuel in ocean tankers, liquefied gas in trucks, or propellant in rocket engines, all of which have slightly more serious consequences than needing to put your shirt to wash!