16 Aug 2016 How to best stop hot drink spills

Walking backwards while carrying your coffee is one solution, but ultimately this causes more spillages than it prevents. Covering your americano with a foam works too, which is good news for cappuccino lovers but not for anyone else.

The most practical way to prevent your coffee from spilling, scientists say, is to hold it from above with a claw-like grip.

Coffee’s propensity to spill is particularly mysterious because wine does not spill anything like as much, even though the liquid itself encourages unsteady walking.

A South Korean researcher has identified both the problem and a solution.

“When a half-full bordeaux glass is oscillated sideways at 4Hz, calm waves of wine gently ripple upon the surface,” Jiwon Han wrote in the journal Achievements in the Life Sciences. “When a cylindrical mug is subject to the same motion, it does not take long for the liquid to splash aggressively against the cup and ultimately spill.”

The 4Hz oscillation was chosen to mimic the effects of walking, and it conclusively showed that in a coffee mug, but not a wine glass, some sort of resonance effect was set up — a wave of a specific frequency that bounces off the sides and increases in amplitude.

Further experiments by Han, from the Korean Minjok Leadership Academy, confirmed that this was the case. Walking set off waves in the mug, and the “second harmonic” of those waves — a wave with double the frequency — resonated to produce spillage.

One way to prevent this would be to serve coffee in wine glasses, or with foam on top. Assuming that the mug is here to stay, and that most adults are unwilling to subsist on cappuccinos, the only other solution is to change the waves.

That is where the claw grip comes in. In carrying the coffee from above, the wrist acts as a pendulum, damping the waves. Experiments proved it stopped the sloshing.

What if the mug is too hot to hold this way? “By walking backwards, we are able significantly to change the frequency characteristics of our hand motion,” Han says.

He concedes, however, that “a few trials will soon reveal that walking backwards drastically increases the chances of tripping or crashing into a colleague also walking backwards”. [No….! Ed]

Source: The Times UK