Why is ice so slippery?

Hook

Why and how is ice so slippery? Most solids aren't. You can walk on rock, wood or glass without sliding. But step onto ice, and your feet can fly out from under you. Scientists argued about why for more than a century.

Pressure

The classic textbook answer was pressure melting. The idea was that your weight squeezes the ice, melting a thin layer of water you slide on.

Wrong

But the math doesn't work. Even on a thin skate blade, your weight only lowers the melting point by a few degrees. That can't explain why ice stays slippery when it's far below freezing.

Friction

Another idea is friction heating. As a skate or shoe slides, rubbing creates heat that melts a little ice. That helps once you're moving, but it doesn't explain why ice is slippery even when you're standing still.

Surface

One leading explanation today is the surface itself. The molecules on the very top of ice aren't locked into the crystal as tightly as the ones below. They form a thin, loosely bound layer that behaves a bit like a liquid.

Rolling

Some research suggests those surface molecules can even roll around like tiny ball bearings. Either way, that slick top layer is what makes ice so easy to slide on.

Cold

Temperature matters too. Lab tests found ice is slipperiest around minus seven Celsius, about nineteen Fahrenheit. Warmer ice gets soft, and much colder ice gets grippy. That's why speed skating rinks are kept right around that temperature.

Close

So ice is slippery mostly because its surface molecules are loose and mobile, not because your weight melts it. ThatsWhyHow.