A new study revealed why a sleepy caffeine fiend is more likely to spill a coffee than a latte.
A team of scientists believe the secret behind the phenomenon is all in the foam, the American Institute of Physics reported. Researchers found even a minimal layer of bubbles can significantly hinder the sloshing motion of the liquid, preventing spillage. The findings could benefit more than just clumsy caffeine addicts; they could have applications in creating safer transport methods for liquefied gas in trucks and propellants in rocket engines.
Emilie Dressaire, now an assistant professor of mechanical and aerospace engineering at the New York University Polytechnic School of Engineering first noticed the phenomenon when she was handed a latte at Starbucks and informed that she probably wouldn't need a stopper to keep it from spilling; she then observed the same thing occurred in bubbly beer.
"While I was studying for my Ph.D. in the south of France, we were in a pub, and we noticed that when we were carrying a pint of Guinness, which is a very foamy beer, the sloshing almost didn't happen at all," said Alban Sauret, who is currently a researcher at the French National Center for Scientific Research (CNRS).
To make their findings the researchers built an apparatus that allowed them to measure the dampening effect of the foam. The device consisted of a narrow rectangular glass container that was filled with a solution of water, glycerol, and Dawn dishwashing detergent. The team injected air at a constant flow rate through a needle at the bottom of the container, creating uniform layers of bubbles.
"The dishwashing foam is very stable, which allowed us to conduct the experiments without the bubbles disappearing," said François Boulogne, another member of the team.
The team looked at the effects of two different types of movements on the bubbly solution by jolting the apparatus with a side-to-side motion or rocking it back and forth; the results of these movements was recorded with high-speed cameras.
The study showed five layers of foam were enough to decrease the height of the waves by a factor of 10, but additional layers did not do much to increase dampening. The researchers believe this effect occurs because the foam reduces the energy of the sloshing motion through friction with the sides of the container.
The findings could also apply to the transportation of hazardous liquids like oil and liquefied gas in large tankers; this is because the sloshing of these solutions can exert enormous pressure on the walls of the transportation container, causing dangerous ruptures and other problems.
The findings were published in a recent edition of the journal Physics of Fluids.
