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Next time you spill a little, let the coffee dry before wiping it up. You’ll notice that after it dries there is a darkish ring around the very edge of the spill, whereas the middle disappears almost entirely. What’s going on here? Robert Deegan and Sydney Nagel at the University of Chicago looked into this phenomenon, and they discovered something pretty interesting. The coffee puddle leaves a ring because it doesn’t simply dry where it sits. As the spill begins to dry, it actually creates its own outward motion, drawing the insides of the puddle toward the edges.
下一次你灑出一點咖啡，在擦掉前讓咖啡變干。你會注意到，咖啡干后在溢出的邊緣處有一圈淺黑的邊，而中間的咖啡幾乎全揮發了。這到底是怎么回事？芝加哥大學的羅Robert Deegan 和Sydney Nagel研究了這一現象，他們發現了一些非常有趣的事。咖啡滴不是簡單地揮發掉，它實際上產生了自身的向外運動，將水滴中間的咖啡推向邊緣。
