Tag: capillary action

Why Do Coffee Rings Form? Because the Grounds are Round

By Veronique Greenwood | August 17, 2011 1:00 pm

coffee ring
Those dark rings in the bottom of your cup arise from fundamental physics.

What’s the News: Some of the most mundane things in life—drinking through a straw, for instance, or washing your hands with soap—are the results of some really neat physics. Today, scientists are adding another item to that list: The ring that forms around a drying drop of coffee. A team at University of Pennsylvania has discovered that that brown ring is a result of the shape of the particles floating in your coffee—and if you squash them out a little, the coffee ring disappears.

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CATEGORIZED UNDER: Physics & Math, Top Posts

Hummingbirds Are Not Sipping Straws. They're Doing Something Much Weirder.

By Veronique Greenwood | May 4, 2011 9:43 am

What’s the News: Hummingbirds have been keeping a secret, now revealed by high-speed videos: their tongues are nothing like straws. They’re much more like mops.

Those dexterous helicopters of the sky (and mascots of this fine news aggregator) are known for consuming large quantities of flower nectar—as much as 14 times their body weight in a day—to power their speedy metabolisms (when your heart beats more than 1,200 times a minute, you’ve got to keep gobbling that fuel). Researchers had always thought that hummingbird tongues, which are forked, functioned like a coffee straw, with two slender tubes using capillary action—the force pulling liquid up the sides of a tube—to drink. But new video evidence shows the two halves of hummingbird tongues scooping up the fluid like tiny hands, knocking the straw theory out of the running.

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