Let's Talk About: Slippery ice

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Have you ever slipped on ice? Gone ice skating? Anyone can tell you that ice is slippery. We have to be careful of ice while driving in the winter, and we use salt to melt ice on our sidewalks. But why ice is slippery is a question that has been difficult to answer. To understand why ice is slippery we need to know how it is formed.

When water freezes if forms a six-sided crystal. That's why snowflakes have six sides. Ice crystals grow as more water freezes on the outside. Because of this, English scientist Michael Faraday thought that a thin film of water existed on the surface of a block of ice. He thought that water was present even at extremely cold temperatures. He came to this conclusion by pressing two blocks of ice together and noticing how they froze together. Unfortunately, the technology did not exist in 1859 for Faraday to test his theory. It would take more than 100 years for his idea to be verified.

Over the years other people have tried to explain why ice is slippery. Some thought that standing on ice melted the surface because of pressure. Others thought that friction caused the ice to melt. Neither of these ideas fully explained why ice is so slippery. Some scientists gave Faraday's idea another look.

It turns out Faraday was right. Modern scientists using X-rays discovered that ice really does have a very thin liquid surface. Surprisingly they found a thin liquid surface on other materials. Even some metals have a very thin liquid layer. Does this mean that someday you might be able to skate on steel instead of ice? We still don't know, but maybe one day we will. One of the great things about science is that we are always learning. As long as we are curious we will keep discovering amazing things.


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