Why Is Ice Slippery?
It is hard to walk on ice because its smooth, frozen surface causes you to slip. Ice is slippery not only because it is smooth but also because it melts under the pressure of your weight and becomes wet.
The slick film of water offers little resistance, or friction, and you slide easily over the ice. (When we ice skate, we aren’t skating on the ice itself, but on a slippery film of water between the ice and the skates.) In very intense frost the ice may become so cold that it will not melt under ordinary pressure. In that case, ice is less slippery, and walking on it is easier.
The other theory is that ice is just slippery, because the outermost layer never turns to a solid. According to this theory, the water molecules at the surface of the ice move more, because they’re at the edge and there aren’t any molecules above them to help keep them in place. As a result, the outermost layer stays in a liquid state even at temperatures way below freezing.