why skating is possible on ice using phase diagram

9.3(a) is adapted from Phase Diagrams of Binary Nickel Alloys , P. Nash As shown in Figure 1, you may notice from the phase diagram that the freezing point (i.e. [1] Colbeck, S. C. (1995). It can be used to cool food and keep it fresh. Physics Today, 58(12), 50-54. Questions/comments about the content? Figure 2. We clearly know that it’s impossible, and that’s why the melting caused by pressure change is not a convincing reason to explain why we can skate freely on ice. As we skate, the contact area between the blade and the ice surface is very small, and the body … Then, what is the main reason for the ice to melt? How the Science of Physics makes it possible to ice skate The physics theory behind ice skating is pretty neat. Let’s walk through a theoretical example. Prof. Tim Leung 梁承裕教授 When I first started to teach myself skating, like all beginners I took this to mean that I would deploy the same walking pattern on the ice, without knowing about using the edge of the blade to dig into the ice. Then, during the spin, we bring our arms in close so that, since conservation of angular momentum holds (i.e. Figure 1 shows the simplest of two component phase diagrams. Copyright © 2014 - 2020 Science Focus, School of Science, HKUST ? Angular momentum is always conserved. Why is ice slippery? We can calculate the following: Iarm = 1/3 * 3kg * (0.6m)2 = 0.36 kg*m2 If the solid/liquid boundary in the phase diagram of water were to slant up and to the right rather than to the left, ice would be denser than water, ice cubes would sink, water pipes would not burst when they freeze, and antifreeze would be unnecessary in automobile engines. her radius). When her leg and arms are out, they are further from the rotating body, so the moment of inertia will rise and the angular velocity will fall. Depending on the intensity and duration of the preceding “In-Season”, the athlete may take one to two weeks entirely off from skating and completes only low intensity off-ice workouts. If you are interested in this topic, you may refer to “Rosenberg, R. (2005). Kit Kan 簡迎曦 We accomplish this by spreading our arms wide and extending our free leg at the base of our jump. Perhaps, the mechanism can be complicated, but intriguing. Figure 4 shows an approximate phase diagram for ice cream mix. At normal atmospheric pressure, water freezes (to ice I, or normal ice) at 32 F or 273 K. js = d.createElement(s); js.id = id; The numerical result shows that, if the rate of heat generation by frictional heating has to be equivalent to that of pressure melting, which is already negligibly small, the length of blade which is in contact with the water membrane must be 15 μm (i.e. A, 172(949), 280-298. In addition, not only did Prof. Weyl from the Pennsylvania State University accept Faraday’s idea, but he also raised a model in 1951 to explain the arrangement of water molecules in both the core and surface of an ice cube. Thinking of the arms and leg as rods, they have a moment of inertia as I=1/3*mr2 (see Wikipedia). And there’s the problem. Prof. Angela Wu 吳若昊教授, Editors 編輯 (1860). So, knowing that our moment of inertia is determined at the instant we lift off the ice, it is obvious that we want the largest moment of inertia to maximize the angular momentum during our spin. Why is ice slippery? Good luck controlling a 540+ rpm jump and landing on the back outside edge of the opposite foot, backwards! Then, according to the conservation of angular momentum, we can decrease our moment of inertia in the air, and thus increasing angular velocity, making us spin faster. I liked the part about the phase diagram. The two pieces of ice then adhere together and become one. Tel: (852) 2358 5776                    Email: sciencefocus@ust.hk The description above sounds reasonable, based on what we’ve learned from school. This activity can be carried out for various reasons, including recreation, sport, exercise, and travel. Also remember that this is the average angular velocity; we will not be able to start this fast (with our leg and arms extended out), so we will be spinning even faster than that when our arms and leg are tucked in. the melting point; the red line in Figure 1) of water decreases as the pressure increases. The difference is that water has more energy than ice … Iout = Itorso + 2*Iarm + Ileg = 0.2 + 2*0.36 + 1.33 = 2.25 kg*m2. We will approximate her torso as a solid cylinder (whose moment of inertia is given by Itorso=mtorso*rtorso2). Perhaps…you may spot some interesting physics in a simple life! In Colbeck’s formula, the contact length between the blade and the ice surface is conversely proportional to the rate of heat generation by frictional heating per unit area. Once you get a push, you continue spinning at the same angular velocity (the speed at which you would be going if your spinning was converted to rolling down a street, for example) if no external forces act on you (note that you always come to a stop; this is indeed because of the external force of friction acting on the bearings, etc.). Ice skating is the self-propulsion of a person across a sheet of ice, using metal-bladed ice skates to glide on the ice surface. This phase starts immediately following the end of the key competitions and lasts for 2-4 weeks. Phase Diagram for Water. It can thus only be also one of the mechanisms that allows us to skate on ice. They add 10kg of mass at a radius r from the cylinder (which in this case is 0.1m i.e. Looking at water’s phase diagram, we can see that at atmospheric pressure (i.e. . It all rests in harnessing angular momentum. Chih-yu Lee 李致宇 So how do they spin in away that leaves us breathless? 3 Coefficient of friction: The rougher the surface, the greater the coefficient of friction. the melting point; the red line in Figure 1) of water decreases as the pressure increases. 4 Liquid-like film: The actual mechanism is still a hot topic for many scientists to investigate. to optimize for minimum friction. In this case, the friction between us and the ice becomes especially small, akin to having a thin layer of water as lubricant. He explained that at 0 °C, for every additional pascal of pressure exerted, it would only cause a decrease of 7.37 x 10-8 °C in the melting point of water, due to the pressure-melting effect. Ice-skating is a common leisure activity that usually takes place at large shopping malls. This enables theoretical and experimental physicists to investigate how much pressure, frictional heating and the liquid-like film on the surface contribute to ice melting respectively under different temperatures. (function(d, s, id) { Water does have the unusual property that solid ice is less dense than liquid water, and ice will melt under sufficient pressure. Terrence Tai 戴煒庭 Sarah Feng 丰志潔 From there, different research laboratories conducted various quantitative research to test this idea in 1950s. Looking at water’s phase diagram, we can see that at atmospheric pressure (i.e. But have you ever stopped to think, how? The components are A and B, and the possible phases are pure crystals of A, pure crystals of B, and liquid with compositions ranging between pure A and pure B. Compositions are plotted across the bottom of the diagram. However, have you ever wondered why we can move freely on ice with a pair of ice skates? All rights reserved. A) the surface of ice is smooth: B) ice is cold: C) the pressure on the ice due to skate melts the ice by lowering its melting point forming a thin film of water: D) the pressure on the ice due to skate raises its melting point: [4] Weyl, W. A. As a result, the freezing point would return to 0 °C, which is the one under standard atmospheric pressure again. Refer to this page for common calculations of moments of inertia. As we skate, the contact area between the blade and the ice surface is very small, and the body weight would concentrate on that contact surface. We have already seen it before, but now we can look in detail to the ice Ih-liquid border. With the advancements in technology, its existence was further confirmed by nuclear magnetic resonance (NMR), proton backscattering and X-ray diffraction. 9*60min = 540 rpm!! Assuming a jump time of 0.5s, a figure skater would need an average angular velocity of. This is only true for water, not any other material. L is constant), as the moment of inertia decreases, our angular velocity increases, thus allowing us to execute more rotations. Does that mean if it gets cold enough that the pressure can’t change the solid to a liquid, skating on ice would be like skating on metal? *Figure Skating image courtesy of Nithin Kadayil. From the public's cumulative knowledge to you, http://bhs.smuhsd.org/science-dept/marcan/apchemistry/h2ophase.gif. I believe many of you must have skated before. This also leads to the subsequent research on the thickness of liquid-like film on the ice surface4. What this means is that the pressure put on the ice by the person's ice skate makes the water go into its denser phase - liquid. Bryan Siu 蕭浩延 [6] Rosenberg, R. (2005). You can probably see where this is going. This is because the pressure exerts on the ice surface would return to normal after the blade passes. 1 atm, or 101 325 Pa in SI unit), and allows the ice in the ice rink to melt, even when the temperature is lower than 0 °C. Assuming they are all of the same length (r distance away), their cumulative moment of inertia is given by mr2. Journal of Colloid and Interface Science, 31(2), 278-286. Ice Skating: An Incorrect Hypothesis of Phase Transitions In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far away as the Oort cloud objects. The mechanism of sliding on ice and snow. ICE tables automatically set … Phase diagram won't really help. One of these special properties is the fact that solid water (ice) is less dense than liquid water just above the freezing point. The phase diagram for water is shown in the Figure below . It may come as a surprise that such sophisticated physical mechanisms underlie a simple leisure activity. DEF. Therefore, if we are skating on a -1 °C ice surface and we want to lower the melting point to -1 °C, by calculation, a pressure of 1.4 x 107 Pa (around 140 atm) is necessary. As the skater sores higher, gravity slows him/her down, until the skater reaches a peak in which there is no more upward movement. as axes are called phase diagrams. Let’s first discuss it at a general level. Also – it’s interesting how it impacts the design of skates, skiis, etc. I guess skiing/snowboarding works the same way. Prof. Simon Chan 陳雲教授 The optimum temperature for figure skating is −5.5 °C and for hockey, −9 °C; figure skaters prefer slower, softer ice for their landings, whereas hockey players exploit the harder, faster ice. Lynn Zhang 張海琳. What are the mechanisms and theories behind? On top of that, the skater has to control their landing so that it is elegant and fluid. Figure skating would be pretty boring if the skaters did spins that us mere mortals could accomplish. According to the article, “Pressure Melting and Ice Skating”, published by a geophysicist, Samuel Colbeck in 1995 in the American Journal of Physics, the decrease in friction could not be due to high pressure-induced reduction of the freezing point. So, let’s assume that of the 10kg each arm is 3kg and the leg 4kg. Your email address will not be published. Physical adsorption of vapor on ice: II. 2 Pressure formula:   (where P is pressure, F is exerted force and A is contact area). If you are holding something heavy in both hands, you’ll notice that if you extend your arms outward during your spin, you will spin slower (but your moment of inertia will increase, thus keeping your angular momentum constant). Faraday therefore discovered that there is a liquid-like film, which plays a key role in the freezing of ice, on the ice surface subsequently. As shown in Figure 1, you may notice from the phase diagram that the freezing point (i.e. According to Bowden and Hughes’s paper published in 1939, they experimented with wood and metals in a research center, which was located at 3 346 m above sea level in Switzerland. While sitting at your couch watching the speed and figure skaters perform their artistic runs at the Olympics, you can only imagine the training they needed to undergo to acquired such precision and elegance in their form. The physics behind ice skating is pretty neat. Introduction. The physical state of a substance and its phase-transition temperatures are represented graphically in a phase diagram. Physics Today, 58(12), 50-54” in the reference list. Pull your arms tightly to your chest and cross the original skating leg over the free leg. Assume a figure skater weighs 50kg (her torso is 40kg, her 2 arms and a leg are 10kg), her radius is 0.1m, her arm span is 0.6m and leg span is 1.0m. R. Soc. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.. Joly never explained how skating might be possible at temperatures lower than −3.5 °C. The thing is, the weight of a human body on an ice skate isn’t enough pressure to induce that melting. Once back on the ice, the focus is on lower intens… That means this skater is spinning 7.5 times faster when her arms and leg are tucked in than when they are extended outward. The Deceived Wisdom: Skaters can skate on ice because their skates melt the surface of the ice, creating a thin lubricating layer. And there’s the problem. The length of a normal blade is 30 cm, and 15 μm is only its 0.005 % (no one would skate with a 15 μm long blade, right?). ICE tables are composed of the concentrations of molecules in solution in different stages of a reaction, and are usually used to calculate the K, or equilibrium constant expression, of a reaction (in some instances, K may be given, and one or more of the concentrations in the table will be the unknown to be solved for). We can therefore skate freely on ice. Conventional wisdom suggests that water doesn’t melt below 0 °C, but such an ingrained belief is indeed the culprit that hinders us in finding another possible reason! A major use of phase diagrams comes about in the prediction of the degree of microsegregation and inclusion (or second-phase) formation. The water membrane freezes again and the ice rink won’t become a pool of water. American Journal of Physics, 63(10), 888-890. Backreaction‘s blog does a great job of thoroughly explaining phase diagrams. The figure below shows an example of a phase diagram, which summarizes the effect of temperature and pressure on a substance in a closed container.Every point in this diagram represents a possible combination of temperature and pressure for the system. Want to receive notifications of new posts by email? Proceedings of the Physical Society. to complete the jump. Assuming that the contact area between the blades and the ice surface is 10 cm2, to exert the equivalent pressure2, the weight of the skater must reach 1400 kg. As the skater falls, the potential energy gets converted back to kinetic energy, and the skater hits the ground with full kinetic energy (i.e. Nevertheless, if it’s true, why wouldn’t all the ice in the ice rink turn into water when there were a lot of skaters? Proc. However, investigations by many physicists revealed that the mechanism of skating was much more complicated, which could be explained in more than one way. How skaters skate on ice using phase diagram of water. The Phase Diagram for Water. Here is the phase diagram of water (From Chaplin's web site, see links). Figure 1. There are several types of energy involved in a figure skating jump. 9.3(a), Callister 7e. So, from the given information. a. Lond. Create a free website or blog at WordPress.com.WPzone.net. As we all know, skate blades are sharp. if (d.getElementById(id)) return; Required fields are marked *, Editor-in-Chief 主編輯 So, to clear up, ice and water can both exist at 0°C at 1 atmosphere. [7] Thomson, J. This confirms the existence of a liquid-like film on the ice surface. So, Iin*ωin = Iout*ωout That is, during a spin, you will always have the same “L” value; thus, if you decrease I (moment of inertia), ω (angular velocity) will increase, and vice versa. As we glide across the ice, we exert pressure on the thin blade, and are therefore creating a small stream of water in our path by melting that ice. Chantelle Sullivan 蘇盈安 You may have heard of “solid-liquid phase equilibrium” when you studied thermodynamics at school1. Next time, when you are enjoying some other leisure activities, don’t forget to think of their “hidden” mechanisms! The phase diagram of an alloy made of components A and B, for all combinations of T and X B, defines the A-B system. Prof. Ho Yi Mak 麥晧怡教授, Prof. Jason Chan 陳鈞傑教授 So we understand how skates glide across ice; but how in the world do figure skaters jump so high, and spin so fast? That’s about the same as a vehicle’s engine’s idling speed. n-alkanes. The water between the blade and the ice is what we really glide across. Skating is possible because of the very small friction felt by a thin blade sliding on ice, in sharp contrast with much larger solid-on-solid friction observed at temperatures well below the melting temperature. Surface forces in liquids and solids. When something changes its state of matter (formally, a phase change), regardless of whatever it is, it remains at it's melting point/boiling point/freezing point UNTIL all of it has changed its state of matter. You will also be entered in a lucky draw to win one Apple iPad mini! Aside from the obvious (ice vs asphalt), to the uninitiated, speed skating on ice and inline skates doesn’t look very different. The skater then explodes up, converting mechanical potential energy through muscle power to kinetic energy. This has long been explained by the existence of a … Nonetheless, the role played by the liquid-like film in ice skating is yet to be confirmed by further research. The reasoning is that due to the high pressure the skates put on the ice, it will melt at temperaturs below 273 K and thus provide a thin film of liquid on which we can skate. Phase diagram for water. We can draw the phase diagram for water. The phase diagram describes the state or phase of a substance according to (1) the pressure exerted on the substance and (2) the temperature of the substance. hard!). duced a liquid film on ice that made skating possible.1 Joly never explained how skating might be possible at temperatures lower than ⊗3.5 °C. Easily accessible tools, diagrams and the choreographic heritage and history of the twin sports of roller and ice skating So, Iin = Itorso + mr2 = 0.2 + (10kg * (0.1m)2) = 0.3 kg*m2. [5] Orem, M. W., & Adamson, A. W. (1969). TWO COMPONENT EUTECTIC SYSTEMS. Note on Professor Faraday’s Recent Experiments on Regelation. (1951). The essence of angular momentum can be described by the following equation: where L is the angular momentum, I is the moment of inertia, and ω is the angular velocity. At 1 atm, the water is solid, but at higher pressures (keeping the temp. We need to calculate the moment of inertia when her arms and free leg (her other leg is on the ground) are out (denoted Iout) and when they are pressed at her sides (denoted Iin). My understanding of ice skating is that it has to do with the pressure of the skate, melting the ice and you skate on the melted water. It was then mentioned as fun fact that you could ice-skate on a planet with lakes of frozen dioxide because that gas has the p (T) -curve the other way round. Throughout this phase, kinetic energy is being converted into potential gravitational energy. Ice skating may be performed on specially prepared ice surfaces (arenas, tracks, parks), both indoors and outdoors, as well as on naturally occurring … Yasine Malki 馬建生 To grasp this speed, we can relate it to the RPM of a car. Skating on ice is possible because . js.src = "//connect.facebook.net/en_GB/sdk.js#xfbml=1&version=v2.7"; Bring your arms forward and jump off the ice at the same time you swing the free leg forward. He put two pieces of ice together so that they are in contact with one another. A phase diagram (or equilibrium diagram) is a diagram with T and composition as axes, showing the equilibrium constitution. fjs.parentNode.insertBefore(js, fjs); It can provide recreation, such as ice-skating. Phase Diagrams • Indicate phases as function of T, Co, and P. • For this course:-binary systems: just 2 components.-independent variables: T and Co (P = 1 atm is almost always used). 15 x 10-6 m), assuming that the skating speed is 5 m/s. 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