A thin film of water
Why Is Ice So Slippery?
Ice is slippery because a very thin layer of liquid water sits on its surface.
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Step 1 of 5
Cold and hard does not mean slippery.
A frozen brick or a cold metal plate offers plenty of grip, so being solid and freezing is clearly not the explanation on its own.
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Step 2 of 5
Ice carries a liquid film on its surface.
The topmost molecules have no neighbours above to hold them in place, so they stay mobile and behave like liquid even well below freezing.
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Step 3 of 5
A thin water layer is what you slide on.
Water between two surfaces is an excellent lubricant, so your foot never really touches the ice — it rides on the film.
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Step 4 of 5
Rubbing and pressure make even more of it.
Sliding generates heat by friction, melting a little more ice and thickening the film, which makes the slide easier still.
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Step 5 of 5
Very cold ice is much less slippery.
Far below freezing the surface film almost disappears, which is why ice at minus thirty feels closer to sandpaper than to glass.
Ice near its melting point is among the slipperiest solids known, but at −30°C it grips well enough to walk on comfortably.
The short version
Ice is slippery because a thin film of liquid water sits on its surface, and that film thins away as the ice gets much colder.
Try it yourself
Compare a wet ice cube from a drink with one straight from a cold freezer. The freezer one is noticeably less slippery to handle.
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