I know that ice is slippery, I don't need to know that. I want to know what makes it so slick.
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A century and a half of scientific inquiry has yet to solve this one. It's clear that a thin layer of liquid water on top of solid ice causes the slipperiness. A fluid's mobility makes it difficult to walk on, even if the layer is thin. But there's no consensus as to why ice—unlike most other solids—has such a layer.
Scientists long reasoned that, since water has the unusual property of being less dense as a solid than as a liquid, its melting point can be lowered with an increase in pressure. While this is true, even the sharpest of skates raises the melting point by only a few degrees. The pressure theory doesn't hold water unless the ice is pretty warm already. Something else must be going on.
Some studies suggest that friction from a moving shoe, skate or tire causes the heat necessary to melt the ice beneath it. A second theory proposes that ice inherently has a fluid layer, caused by the motion of surface molecules that have nothing above to bind to and so move around in search of stability. The reason ice is so slippery may be a combination of these two theories.
Scientists long reasoned that, since water has the unusual property of being less dense as a solid than as a liquid, its melting point can be lowered with an increase in pressure. While this is true, even the sharpest of skates raises the melting point by only a few degrees. The pressure theory doesn't hold water unless the ice is pretty warm already. Something else must be going on.
Some studies suggest that friction from a moving shoe, skate or tire causes the heat necessary to melt the ice beneath it. A second theory proposes that ice inherently has a fluid layer, caused by the motion of surface molecules that have nothing above to bind to and so move around in search of stability. The reason ice is so slippery may be a combination of these two theories.