Why Is Ice Slippery?
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Not because your weight melts it: that lowers the melting point by only a fraction of a degree. A thin liquid-like surface layer (premelting) and frictional melting do the work, and scientists still debate the details.
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Key points
- Pressure melting is the old idea, but a person's weight lowers ice's melting point by only a fraction of a degree, and ice is slippery even near −30 °C.
- Friction: a sliding skate or shoe heats the surface and melts a thin water film.
- Premelting (Faraday): a very thin liquid-like layer covers ice even below 0 °C.
- Newer research suggests loosely bound surface molecules that roll like ball bearings; the full answer is still debated.
Three explanations
| Idea | What it says | Verdict |
|---|---|---|
| Pressure melting | Weight melts the ice under you | Too small: lowers the melting point by a fraction of a degree |
| Frictional melting | Sliding heats and melts a thin film | True for moving skates and feet |
| Premelting (Faraday) | A liquid-like layer exists on ice below 0 °C | Confirmed; explains slipperiness even when standing still |
Why pressure is not enough
Pressure lowers ice's melting point by only about 0.0074 °C per atmosphere. Even on a thin skate blade, a person's weight shifts it by a fraction of a degree, yet ice stays slippery at temperatures far below that, around −30 °C.
Still an open question
Experiments show water molecules at the ice surface are loosely bound and mobile. Some researchers describe them as tiny ball bearings; how much each mechanism contributes is still being studied. Science keeps some questions open, and that is part of the fun.
Try it yourself
Goal: Test the pressure-melting idea: find out when your weight could melt ice, and when it never could.
- Set your mass and choose shoes, skates or one skate edge.
- Compare your pressure with the red mark, the pressure needed.
- Try −0.2 °C on a skate edge: when does it work?
- Make the ice colder and read the mass it would take.
Quick quiz
4 questions. Choose an answer for each, then submit to see your score and the explanations.