As we all know ice is slippery because of melting from pressure and friction. Right? Not really... Harry
http://www.exploratorium.edu/hockey/ice2.html Slippery All the Time Why is the ice slippery in the first place? Is it more slippery when it's "fast ice" or is something else going on? How would a chemist explain the difference between "fast ice" and "slow ice"? We asked Professor Gabor Somorjai of the Lawrence Berkeley National Laboratory these questions and discussed his research into ice. Somorjai's recent discoveries have explained why skaters and pucks slide on the ice. These new findings challenge long-held theories about why ice is 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. Berkeley chemist Michel van Hove, a colleague of Somorjai's, has done calculations which show that skates and pucks do not generate enough pressure to instantly liquefy ice. Somorjai has discovered that ice has a "quasi-fluid layer" that coats the surface of ice and makes it slippery. Even ice that is 200 degrees below zero Fahrenheit (-129 Celcius) or more still has this layer. External Forces? External forces, such as pressure and friction, can melt the ice. But 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. Slippery Layers According to Professor Somorjai, the "quasi-fluid" or "water-like" layer exists on the surface of the ice and may be thicker or thinner depending on temperature. At about 250 degrees below zero Fahrenheit (- 157 centigrade), the ice has a slippery layer one molecule thick. As the ice is warmed, the number of these slippery layers increases. This may help explain in part the difference between "fast ice" and "slow ice." 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. These extra layers would also "soften" a landing for a figure skater--who skates on warmer ice than a hockey player. There is more on the structure of this "quasi-fluid" layer at the beginning of the "Skating" section. But before we get too technical, let's examine how ice is made. <text snipped> Slippery when not wet? The nature of ice was examined in "The Ice" section--including the latest findings by chemist Gabor Somorjai. This new information about ice changes the way we look at skating. For a number of years before Somorjai's research, there was a debate as to whether pressure or friction created the water lubricant that was believed to be required for skating. Most scientists seemed to think that it was pressure. According to Somorjai's findings this is not the case. So what do you skate on? Well, actually you skate on vibrating molecules. Professor Somorjai and his team used new methods developed in the last 10 or 15 years to examine the surface structure and composition of the atoms and molecules that make up the ice. These techniques were developed for high-tech applications--like studying the surface of materials that can be used for magnetic disk drives, for example. Somorjai used these same methods to examine ice. What he found was rather surprising. Somorjai told us, "the structure we determined was an almost impossible structure, indicating that every second water molecule on the surface was missing. Since that was not possible, we decided to go back and understand why [this was the case]." 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. Once Somorjai and his team found this out, they could change the conditions to further study these molecules. Up and down After further study, Somorjai 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 degrees Fahrenheit). This "liquid-like" layer is thought to be what makes the ice slippery. ...
