When a person on skates moves on the ice, he does not run, but glides. The blades of the skates slide smoothly over the surface, obviously not encountering too much resistance. An experienced skater is capable of speeds up to 40 km per hour. The laws of physics are what helps skates to slide and a person to move very quickly on the ice.
Why do skates glide so well? The first thought that comes to mind is simply that the ice is even and smooth. But in reality, there are also smoother surfaces (such as glass) that the skates will not ride on. The whole secret lies in the special properties of water. Water is somewhat different from other substances on Earth. If almost all of them expand when heated, and decrease in volume when cooled, then with water everything happens quite the opposite. If you start to cool water, then for the time being it, like other substances, will shrink, but only until its temperature reaches 4 degrees Celsius. From this point on, the water will begin to expand. And when it turns into ice, it will take up much more space than the liquid required. The structure of the ice molecules is very interesting. They are formed from openwork connections, between which there is a lot of air. To roughly imagine the process of crystallization of water, you can recall the various forms of snowflakes. It is for the very reason that ice contains a lot of air, its density is less than that of water. But when a person comes out on skates, the narrow blades put quite strong pressure on the frozen water. As a result, the ice crystals heat up and collapse, turning back into water. But pressure alone is not enough. It turned out that the ice also melts under the influence of force, which, as it seems, the skater should try to overcome. This is the friction force. After all, the ice only looks so smooth and mirror-like, but in fact the water solidifies very unevenly. The moment the skate slides over the rough, molecularly-scaled surface of the ice, mechanical frictional energy is generated that is instantly converted into heat energy, and this happens very quickly, just as the blade slides over the ice. A thin layer of water forms under the ridge, and it is along this layer that it slides. The layer of water is very thin, and as soon as the blade has left its surface, it immediately freezes again, but this short time is enough to be able to skate.
