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Sasha Cohen, Champion Ice Skater
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. These weren't very efficient,
so they used a long stick to push themselves forward and stay upright. Skates
were originally used for transportation over the frozen rivers 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 Scandinavia.
In the 17th century, canal racing on wooden skates with iron blades was popular
in the Netherlands. Also in that century, James, the younger son of the British
monarch Charles I, came to the Netherlands in exile, he fell for the sport. When
he went back to England, this "new" sport was introduced to the British
aristocracy.
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In the 18th century, ice skating became a world known sport and the Dutch
created skates with longer blades.
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.
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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 from 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.
The source of this article is
Wikipedia, the free encyclopedia. The text of this
article is licensed under the
GFDL
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