layers of bubbles (foam) on top of liquid. Credit: Alban Sauret/Princeton University
Scientists have determined that it is harder to spill a latte than just a regular cup of coffee. The first question is—-wow scientists have a lot of time on their hands. OK forget about the first question. The real question is why? The layers of bubbles on a latte (from the foam, the steamed milk) prevent the coffee from sloshing around. The original observation came from a researcher recalling that Guinness didn’t slosh around as much as other beers (this is the answer to question #1). They did experiments using detergent to form different thicknesses of foam and observed that the foam dissipated the energy from the liquid when it was rocked back and forth. There is even a scientific publication on the subject:
- A. Sauret, F. Boulogne, J. Cappello, E. Dressaire and H. A. Stone. Damping of liquid sloshing by foams. Physics of Fluids, February 24, 2015 DOI: 10.1063/1.4907048