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| 2006/02/23 15:50:52瀏覽681｜回應6｜推薦6 | |
in the snow park on Monday. I showed him how snow acted as a lubricant between our feet and the ground underneath. It was why it was so hard for him to keep balance on the snow. "Like ice skating?" he asked me. Now, it was that one simple question I had hard time to find a simple answer. I remember in the junior high school, there was a very common question about "Why ice is slippery for skaters?" in the physics test. "The pressure exerted along the blade lowers the melting temperature of the top layer of ice, the ice melts and the blades glides on a thin layer of water that refreezes to ice as soon as the blades passes.＂ Zach's father, Dan, who was next to me, answered. Is it really true? No, the answers might not be that simple, even the textbooks are full of it. This was a question changed my way of thinking when I was in junior high school, because I believe ice was slippery even when you wear normal shoes, while the pressure applied on the ice was supposed to be much less than the blades. Interesting enough, two questions that made my teacher felt I was a problematic student were both water related. Another one was "Would water temperature exceed 100 degree C?" I would talk about it in another article if I find time. With this question in mind, I did study hard about physics, and ended up spending one year working for the Insitute of Atomic and Molecular Sciences in Academia Sinica, where surface science was one of the focuses. At that time, most of the research was about Laser, diamond, or equipments related. Water cluster was a new topics that few people were interested in, except crazy people like me. In recent years, things around the ice surface become more popular subjects. Georgia Institude of Technology have used electron-simulated desorption to study chemical reactions on icy surface. When NASA was designing the Mars Lander, the icy surface of Mars was also under serious study. Explaining ice, especially ice surface turn to be a big subject that physists like to talk about. In the thermal dynamics, subjects have multiple forms, other than three, as our convention knowledge. Water, with the unusually property that the solid form is less dense than the liquid form, is helping us to do some interesting researches. The lower dense of ice makes ice to float on water, also means the melting temperature of ice can be lowered below the 32 degree Fahrenheit if pressure is applied on the ice surface. This was how people came up with the explanation. However, it failed in the recent research. Simplily speaking, the melting temerature could be lowered to 31.97 degrees from 32 degrees. Yet, ice skaters still fall at temperature lower than that. After the question was brought up, another explanation people came up was friction. When something touches the ice, the friction helped to melt the ice, and creates a layer of water, which would be slippery. This was close to my explanation of snow was slippery. It was my common sense knowledge, and some physists tried to use this theory to replace the old one from textbook. However, they could not be successful because most people believe that if you want to replace a convention knowledge, you better find it is a good one because ice can still be slippery if a person just stand still on ice. About ten or a little bit more than ten years ago, when surface scienses started to caught attention, one theory was brought up: Maybe the surface of ice is just slippery, with or without any outside impact.This is a typical surface science basic, on the surface, the boundary condition changes since there is no molecule above the surface ones to hold them in place. Thus, those top molecules just stay as unfrozen liquid even the temperature is lower than the frozen point. Now, physists like to tell you that there are two major reasons, but the one in the textbooks is not one of them. In 1850, Faraday put two ice cube against each other, and they fused together almost immediately. And surface scientist started to study the ice surface by applying some high-speed particles on the surface, and study the reaction, a basic surface sciense technique. The founding was that there is still partial water liquid at -235 degrees. In one of the parties we had this year, a friends said a UC-Berkeley professor was using atomic force microscope to study the ice surface and found the friction on the ice was very high. Ice is not really that slippery when you use a tip as big as a few atoms. And this professor believed friction was the primary reason ice is slippery. Scientists call Ice IceIh, the "h" stands for hexagonal, which is how water molecules aligned. One of another variation is called Ice Ic, found in ice crystals floating high up in the atmosphere, forms cubic crystals. At different temperature and pressure condition, the bonds rearranged. I can give you another example of water form, but maybe I should write it in the Science magazine. Simplily speaking, ice is more complicated than what we have been taught. Whether there is water on other planet will determine whether we will continue to explore another planet if one day earth is not going to be in livable condition. How the pressure change the water form, or ice form,will lead us to the next step of our space program, at least the US space program. However, for people in our generation, especially during the Winter Olympics, can we give ourselves a simple answer on: Why ice is slippery? |
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