Why can skates be able to skate freely on ice?

Skating is a popular sport. When you see an athlete wearing a shoe with a knife slip on the sole, sliding like flying on the ice, you will probably ask: the glass surface and the ice surface are equally smooth, why wearing skates can slide comfortably on ice, and not on glass?

The unique thing is that there is always a layer of water between the ice surface and the cutter, which acts as a lubricant, reducing the friction force when sliding. So why is there a thin layer of water under the knife? The important cause is the effect of pressure. Because the melting point of ice drops with increasing pressure, people on ice skates stand on the ice’s surface. Because the contact area between the skates and the ice surface is very small, creating a huge pressure on the ice to lower the melting point of the ice, which makes the ice under the knife slides into a thin layer of water.

But that is not the whole cause. If the bodyweight of a person is 600 N, the contact area between the cutter blade and the tape surface is only 1/1000 m2, the pressure of the slicing knife on the tape surface is about 6×105 N / m2. Under such pressure, the ice’s melting point will decrease by about 10 ° C. Winter in cold countries; the air temperature is usually below minus 30 ° C. It is impossible to rely on the increase in pressure to transform ice into water at such low temperatures. So what causes liquefied ice? When the cutter slides on the ice surface, due to friction with the ice surface, heat causes the contact area’s temperature between the cutter blade and the ice surface to rise, resulting in some liquefaction of the ice into a thin layer of water. Having a layer of water as a lubricant, skates wear skates on, can comfortably slip on the ice.