Saturday, June 05, 2010

The Physics of Hockey

... as in ICE hockey, in case people from other parts of the world get confused since many areas consider "hockey" to be FIELD hockey.

With the Chicago Blackhawks and the Philadelphia Flyers tied in their Stanley Cup championship series, a reporter from the Chicago Tribune decided to ask a University of Chicago physicist on the "physics" of hockey.

A couple of good ones that were asked are:

Q: What principles of physics are at play with the slap shot?

A: Hockey players are taught to swing the blade so it hits the ice about one foot behind the puck. As the hockey stick slides across the ice, it can bend to almost a 30-degree angle. When the blade strikes the puck, it launches the puck at more than 100 miles an hour because of all the energy in the bent stick. If the player cleanly strokes the puck without striking the ice, the maximum speed would be much lower. You really have to get the stick bent.

Q: Why is ice slippery, allowing both skates and puck to glide across it?

A: That question has a long, interesting history that goes back to the 1860s, when (renowned physicist ) Michael Faraday theorized there is a very thin layer of water on ice, demonstrating it by holding two ice cubes together, resulting in them freezing together.

Later there was a theory that skaters could glide across the surface of ice because the pressure of the skater's weight on the blade causes the ice surface to melt. That proved not to be true.

Faraday was right, there is a thin layer of water on the ice surface even at 328 degrees below zero Fahrenheit, but we still don't know why. Because it is so ubiquitous, it's hard to think of water as a weird organic chemical with a lot of strange properties. Ice floats because water in its solid state is less dense than in its liquid state — for example, the opposite of alcohol.

Of course, this is sports. There has to be some silly moments.

Q: Why is Philadelphia Flyers defenseman Chris Pronger such a jerk?

A: There are some questions that physics simply has no answers for. This is one of them.


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