The Science of Hockey
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Read this article and answer the questions which follow:
The Ice:
One of the most unique aspects of hockey is the surface on which the game is played: the ice itself. The players talk about the quality of the ice; they've helped coin the terms "fast ice" and "slow ice." Scientists, on the other hand, are still studying the chemistry of the ice. In just the last few years, there have been major discoveries which have changed our understanding about the nature of the ice.
Fast Ice and Slow Ice
Anyone who has watched a hockey game on television has heard the announcers use the terms "fast ice" and "slow ice," or even "good ice" and "bad ice." What's the difference? Fast ice is harder and colder with a smoother surface, while slow ice is warm and soft and may have a rough surface. For the players, the difference seems to be that "fast ice" is less "chippy" and there is less "snow." Passing and skating are easier when the ice is "fast." The quality of the ice differs during the course of the game and it even changes how teams play the game. Sharks defensemen Doug Bodger told us, "At the end of periods when the ice tends to get 'snowier', and the puck tends to bounce a little bit, you might not try to 'stick-handle' as much-you might just try to get the puck out the zone." In other words, players tend to make a safe play rather than a finesse play when "slow ice" or "bad ice" conditions exist.
Oh, Canada
Certain arenas seem to have better ice than others. Bodger thinks the difference is the hardness of the ice. Rinks in Canada are well known for the quality of their ice. Edmonton in particular was mentioned by Bodger as having fast ice. Why is the ice so much better in Canada? One of the differences may be climate. Bruce Tharaldson, the ice maker at the San Jose Arena, cited deliveries to the arena as a concern. Opening the delivery doors of the arena and letting in heat and humidity is a problem in San Jose, California. This is not as much of a concern for a rink in Edmonton, Alberta, especially in the middle of winter. Apparently, the freezing and refreezing of the ice brings impurities to the surface. Keeping the ice cold is one of the keys to maintaining fast ice. Bruce Tharaldson keeps the temperature of the ice at sixteen degrees Fahrenheit (-9 centigrade) for hockey and twenty-two degrees (-5.5 centigrade) for figure skating. Apparently, the figure skaters prefer softer ice for their landings and the six-degree temperature difference provides that.
Slippery All the Time
Why is the ice slippery in the first place? Is it more slippery when it's "fast ice" or is something else going on? How would a chemist explain the difference between "fast ice" and "slow ice"? We asked Professor Gabor Somorjai of the Lawrence Berkeley National Laboratory these questions and discussed his research into ice. Somorjai's recent discoveries have explained why skaters and pucks slide on the ice. These new findings challenge long-held theories about why ice is slippery. In the past, scientists believed that either pressure or friction melted the ice, creating a water lubricant that allows skates and pucks to slide. Berkeley chemist Michel van Hove, a colleague of Somorjai's, has done calculations which show that skates and pucks do not generate enough pressure to instantly liquefy ice. Somorjai has discovered that ice has a "quasi-fluid layer" that coats the surface of ice and makes it slippery. Even ice that is 200 degrees below zero Fahrenheit (-129 Celcius) or more still has this layer.
External Forces?
External forces, such as pressure and friction, can melt the ice. But Professor Somorjai's findings indicate that ice itself is slippery. You don't need to melt the ice to skate on it, or need a layer of water as a lubricant to help slide along the ice.
Slippery Layers
According to Professor Somorjai, the "quasi-fluid" or "water-like" layer exists on the surface of the ice and may be thicker or thinner depending on temperature. At about 250 degrees below zero Fahrenheit (-157 centigrade), the ice has a slippery layer one molecule thick. As the ice is warmed, the number of these slippery layers increases. This may help explain in part the difference between "fast ice" and "slow ice." As the number of layers increases, the players' skates need to "slosh" through more of these "water-like" layers; more friction occurs in these conditions, slowing the players down. These extra layers would also "soften" a landing for a figure skater--who skates on warmer ice than a hockey player. There is more on the structure of this "quasi-fluid" layer at the beginning of the "Skating" section. But before we get too technical, let's examine how ice is made.
Making ice
So how do you make ice? Ice makers were hard at work long before Professor Somorjai's research was published. Most of their knowledge about ice comes from trial and error, not from scientific journals and textbooks. In our conversation with San Jose Arena ice maker Bruce Tharaldson, we learned a great deal about ice. In addition, we got a chance to see and better understand the legendary ice resurfacer--the Zamboni. Bruce Tharaldson has been involved in the "ice business" for over 20 seasons, starting out making ice for the Minnesota North Stars (now the Dallas Stars). Bruce is responsible for constructing and maintaining the Sharks' playing surface throughout the 82-game season. The season begins in early October and ends in April. The playoffs can extend the season into May or even June. At the beginning of the hockey season, the arena uses an advanced refrigeration system that pumps freezing "brinewater" (salt water) through a system of pipes that run through a large piece of concrete known as the "ice slab." When the "ice slab" gets cold enough, layers of water are applied to it. The first few layers are painted with the hockey markings and the advertisements that you see on (or more correctly "in") the ice. These layers are then covered with 8 to 10 more thin layers of ice. When complete, the ice is only one inch thick! The ice stays in place from September to May. The NBA's Golden State Warriors played on a basketball court that sits on top of the ice. When world famous tenor Luciano Pavarotti visits the San Jose Arena, he sings on a stage above 10,211 gallons (38,652 litres) of frozen water.
Reflection Questions(write your answers on this sheet):
1)In what daily instance does friction affect you?
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2)What two things are rubbing together?
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3) In this particular case, is friction helping to get something done or is it making the work harder? How?
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4)What could you do to either increase or decrease the amount of friction?
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5) Can you think of another similar case in which friction might work the same way?
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