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There are secrets to speed skating

In many winter sports, skaters can be seen with vigorous figures and graceful dancing postures. They can not only move fast, turn flexibly, but also dance gracefully, which is pleasing to the eye. What’s the mystery behind why athletes are so comfortable on the ice?

I don’t know if you have ever thought that athletes wearing ice skates with ice skates can slide quickly on smooth ice, but it is difficult to walk on smooth glass. Why is this?

For this problem, some people have given the explanation: in the process of friction between the ice blade and the ice surface, it is necessary to overcome the frictional force to do work. In this process, mechanical energy is converted into internal energy, which will generate some heat, causing the ice in contact with the ice blade to melt and become water, which to a certain extent lubricates and causes friction between the ice surface and the ice blade The force is greatly reduced, so you can glide quickly on ice in shoes with ice skates, but you can’t glide on glass, because glass can’t be melted and turned into “water”. Is this really the case?

The above explanation is not comprehensive. Because the frictional force of the ice blade sliding on the ice surface is very small, the heat generated by friction alone is not enough to melt the ice in a short period of time. After all, melting requires a process, and the ice is in the melting process. Also needs to absorb a lot of heat.

When a skater slides on the ice, there is indeed a little water on both sides of the skateboard and under it. How does this lubricating water come about and how does it exist?

We all know that under 1 standard atmosphere, the melting point of ice is 0°C; when the external pressure decreases, the melting point of ice will increase; when the external pressure increases, the melting point of ice will also decrease. According to this theory to explain the above question, there is the following answer.

In order to reduce the frictional resistance of the ice to the ice skates and improve the skater’s skating speed and flexibility, skaters usually wear shoes with skates, and the blades of the skates on the shoes are very narrow, and the blades of ordinary skates are only 2 mm wide. , The blade of the figure skate is only 4 mm wide, so the contact area between the skate and the ice surface is very small. Since the pressure of the athlete on the ice surface is certain, the magnitude of this pressure is equal to the weight of the athlete. When the athlete puts on the skates, because the force area of ​​the ice surface is small, the pressure on the ice surface will increase greatly, forcing the melting point of the ice under the skate to drop, so that this part of the ice melts, so there will be a A thin layer of water. It is precisely because this thin layer of water plays a lubricating role that the friction between the skate and the ice surface is greatly reduced, so that the frictional resistance of the athlete moving forward on the ice surface is relatively reduced, so the athlete can move on the ice surface. Walk as fast as you can, and at the same time, you can perform all kinds of beautiful movements at will.

When the ice blade slides over, the additional pressure on the ice surface disappears. Therefore, as long as the outside temperature is below 0°C, the melted water will freeze again immediately. What’s even more amazing is that the skates slide over without leaving scratches on the ice.

This explanation can also be illustrated by simulation experiments. When the ambient temperature is not higher than 0°C (to ensure that the ice will not melt due to the ambient temperature), place a piece of ice on the table, and place a thin wire with heavy objects on both ends on the ice cube, and you will see this A peculiar phenomenon: the ice under the thin iron wire gradually melts due to the high pressure, which makes the iron wire continuously move downward in the ice block. And the water just above the thin wire will freeze due to the reduced pressure. Eventually, the thin wire will pass through the middle of the ice cube, and the ice cube will remain intact.

The above explanation seems to be perfect, but the actual calculation results show that when a person with a mass of 70 kg is standing on the ice with skates, it can only generate a pressure of 3.5 × 105 Pa on the ice surface. The effect of the melting point is not very big, and it can only reduce the melting point of ice by about 0.1 °C. Therefore, this explanation is not entirely convincing.

After that, a new theory was put forward. Scientists have found through experimental research that there is water on ice. Specifically, the surface of the ice is originally very smooth, and when the temperature of the ice surface is above -22°C, there will always be a thin layer of water on the surface that will never freeze.

As early as 1850, the famous British physicist Michael Faraday briefly proposed this theory. In 1996, American scientists proved the theory through experiments. Lawrence Berkeley National Laboratory chemist Sam and physicist Hoover bombarded the ice with a beam of electrons, while using instruments to record the direction and velocity of electrons bouncing off the ice. Unexpectedly, the trajectories of the electrons bouncing back after hitting the ice appeared to be variable, bouncing haphazardly in multiple directions. This means that what appears to be a smooth ice surface is not completely flat.

Sam believes that from the experimental results, the reason why the ice surface is slippery can only be because the top layer of the ice surface is not really condensed, but has a thin layer of water. This layer of water acts as a permanent lubricant. When objects such as ice blades are pressed against the ice surface, water molecules are pressed into the tiny gaps in the ice surface, making the surface of the ice very smooth. As a result, there is less friction on the ice surface, so the blade on the ice surface will be slippery.

The two scientists also found that when the temperature of the ice surface drops below -22°C, the smoothness of its surface decreases dramatically. This is because at such a low temperature, the thin water layer with lubricating function almost disappears, and the smoothness of the ice surface is also significantly reduced, which is basically no different from other solids.