You're tilting a bottle of olive oil over a pan, waiting for the last bit to slide out. Physicists at Brown University now know exactly how long you'll be standing there: over nine minutes.
PhD candidate Thomas Dutta and professor Jay Tang applied the Navier-Stokes equations — the same math used to model ocean currents and airflow over wings — to the problem of draining kitchen containers. Their results, published in Physics of Fluids, calculated how long it takes to recover 90% of the thin film clinging to a container tilted at 45 degrees. Water drains in a few seconds. Milk takes about 30 seconds. Cold maple syrup? A few hours.
They also solved a problem familiar to anyone who cooks with a cast iron wok: after washing it, how long should you wait before tipping out the residual water? Longer than you might think: From Brown University's news office:
After washing a wok, Tang avoids drying it with a cloth because that could wipe away some of the oil seasoning that keeps food from sticking. But he also doesn't want it to stay wet because it could rust. So he has developed his own system for dealing with the problem.
"After I dump out the water from washing, there's always going to be a film of residual water," Tang explained. "So I usually wait a few minutes to let that film of water collect in the bottom, then just dump it again."
The key is waiting long enough for the water to pool before dumping but not waiting so long that the water promotes rust in the wok as it slowly evaporates.
Dutta developed a computer simulation using the fluid mechanics equations to estimate the optimal wait time, which turned out to be around 15 minutes.
"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."
The project grew out of Tang's biophysics lab, where he studies bacteria moving across moist surfaces. "This physics is everywhere in our main research," Tang said. "It just happens to also be the everyday fluid physics of the kitchen." Dutta's inspiration was more personal — his grandmother's determination to get every last drop out of a container.
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