Written by Brian S. (KIS'19)
Edited by Jenny C. (VHS'19)
━━ April 7th, 2018 ━━
With the Winter Olympics coming to a close, I’m sure many of you have enjoyed watching the various events. Personally, my favorite is the halfpipe snowboarding. Watching the athletes do insane tricks, twisting and turning their body in the air, always seems mystifying to me, almost as if they are defying the laws of physics. Surprisingly, there is actually another winter sport that seemingly defies the laws of physics: ice skating. Scientists are still not one hundred percent sure as to how skaters actually skate on the ice. There are multiple theories out there, some being more plausible than others, that attempt to explain how the skaters are able to gracefully glide across the ice.
The Theories Behind Ice Skating
One thing that scientists know for sure is that ice itself isn’t actually slippery. What makes it slippery is a layer of water on top of the ice, which lowers the friction of the surface. This, in turn, causes whatever is on top of the ice to be able to slip and slide, like what can be seen with ice skaters or people slipping and falling on ice. What still baffles scientists is how the water got there in the first place. The theories all address ways that water can be created from ice. It may sound simple at first glance, as ice is just frozen water, but the deeper you dig into the theories, the more confusing they becomes.
The first theory (although it only applies to ice against ice and not ice against skates) comes from English scientists Michael Faraday and James Thomson. You may have heard of the name Faraday while studying chemistry or physics. Michael Faraday was born on September 22nd, 1792 in England. Throughout his life, he was able to make many notable achievements in science, including electromagnetic induction, diamagnetism, and electrolysis. The discovery that we will be focusing on is his discovery of the ability for ice cubes to fuse together. In June 1850, Faraday presented, at London’s Royal Institution, an experiment which showed that two ice cubes, if pressed against each other at freezing temperatures, will combine into one ice cube. James Thomson, a fellow scientist at that time, following up on Faraday’s experiment, proposed that the ice cubes were fusing due to the pressure that they exerted on each other when pressed together. The pressure melts the ice, which creates a thin layer of water that can be refrozen, combining the two cubes. However, Thomson’s theory wouldn’t work for ice skating. Recent studies show that it would take quite a heavy skater in order to melt the ice due to pressure. Faraday thought that there was something else besides the the pressure melting the ice that caused the ice cubes to fuse. He didn’t think that it was pressure that was causing the melting of the two cubes. Faraday hypothesized that a thin layer of water surrounding ice is actually a property of ice. At that time, he had no way of proving this, but this hypothesis is crucial for another theory behind ice skating.
Probably the second most prominent theory behind skaters being able to glide over ice is that friction melts the ice, which creates the layer of water that makes ice slippery. Friction is the force that acts on two things that are touching, so that it stops the two things from moving. Friction affects us daily. In fact, if it weren’t for friction, we would be sliding around everywhere. It allows us to walk, wear things, and hold things. Friction is also able to generate heat. This can be seen when you rub your hands together. If you keep rubbing them together, your hands will feel slightly warmer, due to friction. So, it would make sense that, as the skater is gliding along, the ice skates are creating friction against the ice, which causes the ice to heat up and melt. However, the ice skaters’ blades are only touching each spot of the ice for less than a second. This would not be enough time to melt the ice under the friction of the blade. Another issue with this theory is that ice is still slippery if you just stand on it. If you were standing on top of some ice and someone pushed you, you would slide a little (assuming you were able to keep your balance and not fall over). Even though there is very little friction applied to the ice, the ice is slippery. Although friction isn’t the main reason why ice is slippery, it is one of the key reasons why ice skating works.
Going back to Faraday’s hypothesis, more research has been done on his proposed property of ice: ice fuses when they are pushed together. Now, scientists know that ice actually is surrounded by a layer of molecules in a quasi-solid state or a state in between solid and liquid. On one hand, this membrane is able to keep its shape, just like a solid can stay rigid. However, when pressure is applied, it is able to change its shape, so that it takes the shape of the thing that is applying the pressure, just like that of a liquid.
Now that the meaning of quasi-solid (semi-solid) is clear, you may be wondering why it appears in the first place. The thing layer of water is able to form because of ice’s ability to form strong hydrogen bonds. The inner water molecules are able to be arranged in a crystal lattice, but the outer molecules want to try to make as many hydrogen bonds with each other as possible. In trying to achieve this, the water molecules become “disordered”: a state in which it is less of an orderly crystal lattice and more random, like liquid.
So, this semi-solid layer of ice is the most important factor when it comes to ice skating. The skater’s blade slightly deforms the semi-solid layer of ice, which creates friction in between the skates and the ice, which melts even more ice. This may seem like it contradicts what was said earlier: that friction didn’t create enough heat to melt the ice. However, that was ice, a solid. Instead, we are not talking about the semi-solid layer surrounding the ice, which is much easier to melt because it is already halfway to a liquid. Basically, the skaters aren’t actually skating on top of ice, but instead, they are skating in the water on top of ice.
This hypothesis, ice’s semi-solid liquid layer, is currently the most widely accepted hypothesis today. However, the quasi-solid layer still remains as a hypothesis, and not a fact. No one has been able to prove whether this is actually what happens or not because the layer of water created by the ice skates is too thin and refreezes too quickly to be detected.
━━━━━━━━
Bibliography (Pictures):
━━━━━━━━
Comments