Comments by "Mikko Rantalainen" (@MikkoRantalainen) on "COLD HARD SCIENCE.The Physics of Skating on Ice (With SlowMo) - Smarter Every Day 110" video.

  1. It turns out that ice being slippery is much more than friction melting or pressure melting. The article titled "Why Is Ice Slippery?" by Robert Rosenberg explains this is great detail. The actual cause turns out to be 10–100 nm thick water-like film on water-air surface. And this film like structure appears to form even on air-vacuum surface but then the film is even thinner.
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  2. And they needs lots of experience. To stop on a spot from high speed, you have to have pretty good understanding of the sharpness of your blade, the condition of the ice (how smooth it is, how much snow on top) and the temperature of the ice. Then you just feel the pressure in your feet during the breaking. You start the breaking with knees bent and if you need more stopping power, you press faster towards to ground, if you need less stopping power, you release some pressure and turn the blade a bit towards the 90 degree orientation. If the ice is smooth enough, you can do the breaking movement with the blade nearly perfectly orthogonal to the ice and the breaking power is really low. The blade just skims the surface. However, your weight will go to the outside edge really easily if the ice is not perfectly smooth. When the speed is mostly slowed down (say about 5 km/h or less), you can basically hop on skates during the braking action to instantly stop by pushing the edges into the ice. That will stop the skates and the remaining energy must be transferred to your muscles and pushing you upwards (you still have knees bent, right?). However, if you estimate your speed incorrectly, your muscles are not strong enough to take the instant stop immediately or your knees are not bent enough, and your weight will go the outside edge and you'll fall. It's not dangerous but will look a bit embarrasing.
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