Related Lessons

Putting the Ice in Hockey

• Putting the Ice in Hockey student sheet

• Discuss the other states of matter in which ice can exist. (Ice can be a liquid (water) or a gas.)
• How does the molecular motion differ between a solid, liquid, and a gas? (In solids, the atoms or molecules are closely locked in position and can only vibrate. In liquids, the molecules are more loosely connected and can slide past one another. In gases, the atoms or molecules have more energy and are free of one another except during occasional collisions.)
• Describe the physical characteristics of ice. (Ice is cold, hard, wet, smooth, and slippery.)
• Can you think of any other solids that are as slippery as ice? How does the slipperiness of ice compare to solids such as wood or cement? (Other solids are not as slippery as ice.)
• What do you think makes ice slippery? (Allow students to freely express their opinions.)

• Describe the difference between "fast ice" and "slow ice." (Fast ice is harder and colder with a smoother surface, while slow ice is warm and soft and may have a rough surface. "Fast ice" is less "chippy" and there is less "snow.")
  


• Which kind of ice do hockey players seem to prefer? Why? (Players seem to prefer ice that is "fast" because the passing and skating are easier.)
  


• Where are the hockey arenas located where the ice is better? Why? (Hockey arenas in Canadian cities such as Edmonton are known to have better quality ice. Less heat and humidity get into the arena. This keeps the ice cold, which is one of the keys to maintaining fast ice.)



• How does the ice differ for hockey and figure skating? (For hockey, the temperature of the ice is kept at 16° Fahrenheit [-9° Centigrade] and for figure skating it is 22° Fahrenheit [-5.5° Centigrade]. Figure skaters prefer softer ice for their landings.)



• In the past, what did scientists think caused ice to be 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.)
  


• According to Professor Somorjai and his colleagues, why is the previous theory about why ice is slippery incorrect? (Skates and pucks do not generate enough pressure to instantly liquefy ice. 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.)
  


• According to Professor Somorjai, what may account for the difference between "fast ice" and "slow ice?" (The "quasi-fluid" or "water-like" layer on the surface of the ice may be thicker or thinner depending on temperature. As the ice is warmed, the number of these slippery layers increases. 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.)



• What did Professor Somorjai discover when he first examined the surface structure and composition of the atoms and molecules that make up ice? What did he discover upon further research to indicate what makes ice slippery? (At first, the structure indicated that every second water molecule on the surface was missing. After further study, Somorjai's team found that the "missing" water [or ice] molecule was indeed there, but it was vibrating so rapidly that it was invisible to the technique they were using. Then, he found that these molecules behave like a liquid, but they only move up and down; they do not move from side to side on the surface of the ice. This is an important distinction. If the atoms moved side to side, the "liquid-like" layer would literally become liquid [which is what happens when the temperature rises above 32° Fahrenheit]. This "liquid-like" layer is thought to be what makes the ice slippery.)
  


• Describe the steps involved in making ice for a hockey arena at the beginning of the season. (At the beginning of the hockey season, the arena uses an advanced refrigeration system that pumps freezing "brine water" [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.)



• What is a Zamboni? How does it work? (The Zamboni is a mechanical ice resurfacer. It works by scraping the ice surface and collecting the snow [ice that the been scraped loose.] Next, it "cleans" the ice, by putting down water which flushes the grooves deep in the ice, loosening any dirt or debris. The excess water and dirt is then collected. Finally, the Zamboni puts down a thin layer of heated water that freezes and creates a smooth surface.)

(The "old" theory stated that either pressure or friction melted the ice, creating a water lubricant that allowed skates and pucks to slide. According to Professor Somorjai, skates and pucks do not generate enough pressure to instantly liquefy ice. He found that ice molecules vibrate extremely rapidly, but they only move up and down; they do not move from side to side on the surface of the ice. This creates a liquid-like layer on the surface of the ice. It is this layer that makes ice slippery. The students' illustration should show the molecules on the top layer of the ice moving very rapidly up and down.)


Extensions
The following Internet resources can be used to further explore topics related to ice and the science of hockey.

• The Physics of Ice Skating uses ice skating to explore several basic principles of physics, including Newton's second and third laws, kinetic and potential energy, friction, and torque. It also includes links to other websites related to physics and ice skating.


• Ask Mr. Science addresses the interesting question, "Why is ice slippery?" Students can read and discuss the response, which is listed below.


This is an interesting question because a few years ago I would probably have given the wrong answer. The old story was that the pressure of your skate would be enough to cause the ice under the blade to melt, or friction would melt the ice under your skate or ski. Wrong! Recent research (1999) has shown that there is a thin film of liquid on the surface of the ice, even at temperatures far, far below freezing. This is true for ice, but also for other materials. So ice is slippery because of this layer of water which is always there, regardless of pressure or friction.