Good news for romantic comedy heroines with a clumsy streak (i.e. all of them): scientists have found the type of coffee least likely to spill. Lattes are apparently much easier to carry incident-free than your standard drip coffee – which turns out to be aptly named.
Researchers Emilie Dressaire, from the New York University Polytechnic School of Engineering, and Alban Sauret, from the French National Centre for Scientific Research, had both noticed that foam seems to make some drinks less prone to spillage.
So they decided to test to see if they could find a scientific formula to explain this effect. They and their colleagues built a device that was made up of a narrow glass container that could be rocked back and forth or side to side. They filled this with a mix of water, dishwashing liquid, and glycerol (to make it more viscous than mere water). They also injected air at a constant flow into a small opening at the bottom of the glass, in order to create uniform layers of three millimetre bubbles.
Then they tried jolting the device quickly from side to side and slowly rocking it backwards and forwards, recording the ‘waves’ that resulted. They concluded that five layers of foam decreased the height of the waves by a factor of ten, although more than five layers didn’t have any additional effect. They think the friction of the foam touching the sides of the cup slows down the sloshing liquid below. And not just for lattes – this also explains why Guinness is easier to carry than beer. (If not necessarily easier to drink…)
But their experiment isn’t only a ‘huh, weird’ for the clumsy and thirsty. It has potential applications for the transport of hazardous liquids like oil and liquefied gas, and the researchers hope it will lead to finding safer ways to transport those fluids in future.