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Ice skating

From Academic Kids

Ice skating is traveling on ice with skates, narrow (and sometimes parabolic) blade-like devices moulded into special boots (or, more primitively, without boots, tied to regular footwear). It is mainly done for recreation and as a sport.

It is possible on canals and lakes, etc. after it has been freezing for some time, and at indoor and outdoor skating tracks and areas with artificial cooling. The skating rink regarded as the world's longest (about 8 kilometres long) is the Rideau Canal located in Ottawa, Ontario, Canada.

In some countries with a temperate climate, e.g. the Netherlands, frozen canals and lakes are fairly rare, but skating is popular where these are encountered.

Contents

History

Ice skating has been believed to be started in Sweden over twelve-hundred years ago by the Vikings. The runners, made of bones, were ground down until they formed a flat gliding surface, and thongs tied them to the feet. The blades were polished oxen or reindeer bones. Skates were originally used for transportation and later used for fun. Skating has been found to date back to 50 B.C. It was most common to skate where there are long, cold winters especially in places like the Netherlands. In the 18th century, ice skating became an international sport.

How it works

Ice skating works because the metal blade at the bottom of the ice skate boot can glide with very little friction over the surface of the ice. However, slightly leaning the blade over and digging one of its edges into the ice ("rockover and bite") gives skaters the ability to increase friction and control their movement at will. In addition, by choosing to move along curved paths whilst leaning their bodies radially and flexing their knees, skaters can use gravity to control and increase their momentum. They can also create momentum by pushing the blade against the curved track which it cuts into the ice. Skillfully combining these two actions of leaning and pushing - a technique known as "drawing" - results in what looks like effortless and graceful curvilinear flow across the ice.

In the past, the explanation for the low friction between the metal blade and the ice surface was that the pressure exerted by the blade on the ice caused the surface of the ice to melt. It was believed that this thin layer of water allows the blade to glide over it with very little friction. This hypothesis predicts that the greater the pressure exerted by the blade, the slipperier the surface of the ice will become.

However, it was found that the classic explanation was not the whole story. Experiments have shown that the pressure exerted by the blade has no effect on the amount of friction generated. The easiest proof of this is that a small child can skate on the ice as frictionlessly as a much heavier adult ice skater. The pressure required to melt the ice in this manner is about 10 times more than any ice skates generate, and the ice would shatter underneath the skates at that point.

Further research in materials revealed the true nature of skating. Because the atomic structure of ice is a crystalline structure, it turns out that having this structure abruptly stop when it reaches the top of the ice is not the most entropically favorable form. Instead, there is always a thin film of liquid water ranging in thickness from only a few molecules to thousands of molecules on top of the ice. This allows a smoother transition form the structured ice to the completely random structure of the air molecules. The thickness of this liquid layer depends almost entirely on the temperature of the surface of the ice (higher temperatures give a thicker layer), and the liquid layer disappears around -20°C (-4°F). At temperatures below -20°C, ice skating becomes impossible because friction drastically increases and it feels like skating on glass. Experiments show that ice has a minimum of kinetic friction at -7°C, and many indoor skating rinks set their system to a similar temperature.

External links

See also

A number of sports are based on the principle of ice skating:

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