Ice, unlike most solids, is slippery. That is why it is possible to skate on ice but not on solids such as marble or steel. Why is ice slippery? Incredible as it may seem, physicists have been perplexed by the slipperiness of ice and have not found a fully acceptable explanation of it.
One idea is based on the fact that whether a substance exists as a solid or liquid depends on the pressure exerted on it. Increasing the pressure lowers the freezing point of water, so it is a liquid even at temperatures below 0 degrees centigrade. Thus, when a skater moves on ice, the pressure from the skater's weight on the blade of the skate causes the ice immediately under it to melt. The skater slides on this tiny patch of water, which is continuously created as the skate moves forward.
The problem with this idea is that the pressure from even a heavy skater would change the freezing point of water just a tiny fraction of one degree. However, the temperature of ice is often well below the freezing point. On a cold day, the ice might be 10 or 20 degrees below freezing. So the minuscule effect of the skater's pressure would not be sufficient to cause the ice to melt. Yet, of course, it is possible to skate in very cold weather.
Another idea is that the slipperiness of ice is due to friction between the skate and the ice. Friction creates heat, and experiments have shown that the frictional heating caused by an ice skate moving across the ice is enough to create a thin, watery layer on top of the ice. The skater glides on this thin layer of melted ice.
The problem is that frictional heating occurs only when one thing is moving against another, but ice is slippery even when there is no motion. If you are standing on ice and tilt a little to one side, then, even though your skates are not moving, they will slip out from under you. So the ice is slippery even before there is any motion that melts it through friction.