Ice, Ice, Baby: Why Is Ice Slippery?
How does water turn into ice? Why is ice sometimes slippery and other times sticky? Why is it so cold? Why does it float? How are icicles made? Why are icebergs mostly underwater? What was the ice age? We'll get answers to all of those questions with help from Celeste Labedz of the California Institute of Technology. And we'll take a trip to the world's largest skating rink.
"Why are icebergs mostly underwater?" -Aiden, 6, Edmonton, Alberta, Canada
"It's because of their density," says cryoseismologist Celeste Labedz. Density is how much mass is in a volume of space.
"If you have a rock and a piece of Styrofoam that's the exact same size," she says, "the rock will be much heavier because it has a higher density. If you put something in water that's more dense than water, like a rock or metal, it will sink right to the bottom. But if you put in something that's less dense, like Styrofoam or a basketball, it will float at the surface. Icebergs float with only a little bit above the surface because they're only a little less dense than the water. The reason for that difference is that the H2O molecules in water and ice take up just a little bit as a solid crystal, the ice, than they do as a flowing liquid. This density difference means that any piece of ice in water will have 90 percent of its volume below the surface and 10 percent above."
It's all about the density and not about the size. One way you can observe this yourself, without having to travel to one of the poles, is to put an ice cube in a glass of water. You'll have a mini iceberg in your glass and you can see the same principle at work: an ice cube has the same fraction of its ice above the surface as an iceberg!
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