Down to the Last Drop: Physics Answers a Kitchen Question
How long does it take for the last drop of milk or oil to drip out of the bottle? US scientists have probed this everyday conundrum.
How long does it take for the last drop of milk or oil to drip out of the bottle? US scientists have probed this everyday conundrum.It makes sense to squeeze every last drop of milk into our coffee and drizzle the remains of our expensive olive oil over our salad — so we stand our kitchens, holding bottles or cartons at awkward angles, waiting and watching with varying degrees of patience.
How long do we have to wait? That’s what two physicists at Brown University in Providence, in the US state of Rhode Island, wanted to find out. Their findings were published in the journal Physics of Fluids.
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Thomas Dutta, a PhD candidate, recalled how his grandmother struggled with getting the last few drops out. And his physics professor, Jay Tang, also knew how it felt to stand in his kitchen, wondering how long it takes for the water to drain off his cast-iron wok after washing it.
Probing everyday science
Tang usually researches the biophysics of bacteria — more specifically, how single-celled organisms move and bacteria swarms spread across wet surfaces. This research requires a thorough understanding of fluid mechanics. To help Dutta grasp these concepts, Tang decided to focus on everyday physical phenomena.
Take, for example, the problem of washing his wok. The professor doesn’t dry it because that could remove the vital oil layer that prevents food from sticking. But, if the wok stays wet for too long, rust could form as the remaining water evaporates.
"After I dump out the water from washing, there’s always going to be a film of residual water," Tang said. "So I usually wait a few minutes to let that film of water collect in the bottom, then just dump it again."
But are those few minutes enough for as much of the residual water as possible to collect so it can be poured out? To find out, the researchers set out to calculate the waiting time required for liquids to drain. Among other things, they examined milk, olive oil, maple syrup and the water that collects in Tang's wok.
Fluid mechanics and maple syrup
Tang and Dutta calculated the required time using Navier-Stokes equations, which measure the motion of liquids and gases, such as water, oil and air.
After the physicists had hypothesized how long it would take for the liquids to flow down an inclined surface, they tested this in experiments. They let the liquids trickle down a plate tilted at a 45-degree angle. By weighing the amount that had flowed off, they determined when 90% of a liquid had drained.
The experiments essentially confirmed their hypotheses. Water drained away within a few seconds. For low-viscosity liquids such as milk, it took about 30 seconds for 90% of the thin liquid film to drain. Thicker olive oil, on the other hand, took over nine minutes. Cold maple syrup took several hours.
And the "wok problem"? Using fluid dynamics equations, Dutta developed a computer simulation to determine the optimal waiting time for collecting the remaining water in the wok.
"I was surprised and actually a little disappointed," Tang said. "I usually wait only about one or two minutes, but it turns out that I need to be a lot more patient." Dutta’s calculations showed that it takes about 15 minutes for 90% of the residual water to collect at the bottom of the wok.
A German award for 'playful' science
An award has been created for scientists who work to answer quirky questions. The Mario Markus Prize for Ludic Science honors research in the field of natural science that stands out for its inventive curiosity. Ludus comes from Latin and means "play."
Worth €10,000 ($11,600), the prize has been awarded by the German Chemical Society since 2022. The prize was initiated by the German-Chilean physicist Mario Markus, who conducted research at the Max Planck Institute for Molecular Physiology and was influential in the sphere of "ludic science."
Discoveries that have left their mark on how we live often emerge from playful experimentation and a dose of curiosity.
The element of chance helps researchers
Alexander Fleming discovered penicillin only because spores from mold of the genus Penicillium accidentally landed on bacterial cultures he intended to use for experiments. Fleming noticed that many of the bacteria died as a result.
Charles Nelson Goodyear accidentally dripped a mixture of natural rubber and sulfur onto a hot stove top — afterward, the rubber became significantly more elastic, robust and stable. Just like that, the vulcanization of rubber had been discovered.
And we have a woman named Kay Zufall to thank for Play-Doh. The kindergarten teacher realized that a moldable wallpaper cleaner was popular for entertaining children — and coined the name Play-Doh, now used in nurseries and playrooms around the world.
This article was originally written in German.
(The above story first appeared on LatestLY on Mar 21, 2026 11:10 PM IST. For more news and updates on politics, world, sports, entertainment and lifestyle, log on to our website latestly.com).