Scientists Crack The Physics of Coffee Rings

"A lot of simple things in science turn out to be quite complicated. Take, for example, coffee: You may have noticed that a spilled drop of coffee doesn't dry as a brown blob, but rather as a clear blob with a dark ring around the edge."

"It's taken physicists more than a decade to figure out why this effect, known technically as "the coffee ring effect," happens. But now they think they have an answer."