Montshire Minute: Ice Hockey

Originally aired during the week of March 8, 1999

Monday

The mystery substance of the day is colorless, odorless, and tasteless. It's also very slippery, and without it there would be no slapshots, breakaways or power plays. We are talking ice, here, ladies and gentlemen, so watch your step! Because this week, we're going to be chipping away at the science behind skating and the sport of ice hockey! Perhaps you've had a chance to get out on the ice this winter, on a frozen pond or lake. And perhaps you've also skated on an indoor rink with artificial ice. Ever notice the difference between these ice surfaces? You might notice that natural ice seems harder and you can skate with less effort. Experienced skaters refer to "fast" ice as hard and cold with a smooth surface. "Slow" ice is softer and may have a rough surface. You may have to push harder in softer ice to propel yourself forward. Or backward. Or . . . on your backside!

Tuesday

We're looking at the science of ice hockey on the program this week and before we can unleash our slapshot, we need to know a little bit more about the science of skating. The blades of the ice skate are narrow and sharp, which means very little surface area actually makes contact with the ice. The blades are also exerting a tremendous amount of pressure on the ice below. Until recently, it was thought that this pressure, combined with the friction between the blade and ice, causes some of the ice to melt directly below the blade. The theory goes that the thin film of water created by this melting helps the skater slide smoothly over the ice. More recent research suggests that ice is always coated with a semi-fluid layer - even ice cooled to 200 degrees below zero Fahrenheit!

Wednesday

Pressure can cause ice to melt. It has been assumed that the pressure exerted by a hockey player melts the ice under the blade of the skate just long enough to create a "slippery layer" that allows for maximum glide. After all, a professional skater can exert a pressure of 700 pounds per square inch! But researchers from Berkeley have suggested that you don't need to melt the ice to skate on it - the ice itself always has a "slippery layer." This layer gets thinner as the temperature cools - at about 250 degrees below zero Fahrenheit, the ice has a slippery layer one molecule thick. The number of slippery layers seem to increase as the temperature warms. This may explain the difference between what hockey players call "fast ice" and "slow ice": the warmer the ice is, the harder players have to work to push off and gain speed. Players in the National Hockey league can skate over 20 miles per hour on the ice!

Thursday

The Exploratorium Science Center in San Francisco looked into the forces at work when a National Hockey league defenseman unleashes a 100-mile per hour slapshot. A slapshot begins when the player raises his stick high and swings it forward with one quick movement, slapping the puck with the blade of the stick. The power for the shot comes in the quick weight transfer from the back leg and through the hands to the stick. A high speed camera on a slapshot fired off by San Jose Shark Jeff Friesen shows that the player's stick actually comes in contact with the ice about a foot before the stick touches the puck. This causes the stick to bow slightly. This "bow" or bend in the stick is released about the same time as the stick makes contact with the puck, releasing even more energy into the puck.

Friday

Back in the old days, ice hockey was purely an outdoor sport, played on natural ice. And unless you were from Canada or the northern part of the US, hockey sticks were pretty useless unless you wanted to use them as tomato stakes. But today, thanks to modern icemaking technology, hockey can be played pretty much anywhere, even in sunsplashed cities like San Jose and Dallas. Most arenas use a refrigeration system that pumps freezing "brinewater" (salt water) through pipes that run through a large concrete slab. When the slab gets cold enough, a thin layer of water is poured on it. When the water freezes, the process is repeated over and over, creating an ice sheet strong enough to skate on. Still, the ice surface of an indoor rink may only be an inch thick! To find out more about the science hockey, check out the San Francisco Exploratorium's website at http://www.exploratorium.edu