Olympic Physics: Ice, Ice, Baby
Tim Gay is a physics professor at the University of Nebraska-Lincoln. He’s known for his videos explaining the physics of football. So we asked Dr. Gay to explain the physics behind winter Olympic events. Figure skating and hockey are just two of the sports that require a solid sheet of ice. In this report, Dr. Gay explains what makes ice slippery.
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[00:00:00.530]From figure skating to ice hockey to the monobob,
[00:00:04.890]the Winter Olympics have one central theme,
[00:00:07.690]the rapid movement of blades, runners,
[00:00:11.090]skis, or discs across solid water,
[00:00:15.990]known to most of us as ice.
[00:00:18.610]The physics question here is
[00:00:20.930]why is ice so darn slippery?
[00:00:23.810]At the first level, it's simple.
[00:00:27.010]Ice is slippery because it almost always
[00:00:29.040]has a thin layer of liquid water on its surface.
[00:00:32.210]Water reduces the friction
[00:00:33.710]of whatever material it happens to be sitting on.
[00:00:36.800]But if it's cold enough for ice to form,
[00:00:39.170]why doesn't the water on top freeze, too?
[00:00:42.040]You may have been told that the ice melts
[00:00:44.070]because of the pressure exerted on it by, for example,
[00:00:47.000]the blade of the skate.
[00:00:48.860]The movement of the blade produces a thin film of water
[00:00:52.240]over which the skate slides smoothly.
[00:00:55.580]This explanation turns out to be wrong.
[00:00:58.030]Recent developments in our understanding
[00:01:00.060]of the molecular structure of ice
[00:01:02.010]provide the correct answer.
[00:01:04.830]In solid ice, the water molecules are arranged
[00:01:07.820]in a strong lattice due to the bonding
[00:01:10.140]between molecules caused by their hydrogen atoms.
[00:01:13.750]When we move up to the surface, though,
[00:01:15.730]these bonds weaken because the top layer of molecules
[00:01:18.810]have nothing to bond to above that surface.
[00:01:21.750]The last few layers of water molecules don't stick together
[00:01:25.390]and return to their original form, liquid water.
[00:01:28.920]This thin layer is what makes ice slick
[00:01:31.560]and makes the Olympics so fun to watch.
[00:01:34.430]Now that you know the physics
[00:01:35.810]behind all these great winter sports,
[00:01:37.820]be sure to tell a friend at the next party you're at.
[00:01:40.690]That should be enough to break the ice.
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