They add 10kg of mass at a radius r from the cylinder (which in this case is 0.1m i.e. Prof. Ivan Ip 葉智皓教授 Pressure melting and ice skating. As the skater sores higher, gravity slows him/her down, until the skater reaches a peak in which there is no more upward movement. Perhaps…you may spot some interesting physics in a simple life! One of these special properties is the fact that solid water (ice) is less dense than liquid water just above the freezing point. To finish it off, according to conservation of angular momentum, Lin = Lout You can probably see where this is going. Introduction. [7] Thomson, J. 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 we all know, skate blades are sharp. Ice-skating is a common leisure activity that usually takes place at large shopping malls. Rotate one and one-half revolutions in the air. 9*60min = 540 rpm!! Ice skating may be performed on specially prepared ice surfaces (arenas, tracks, parks), both indoors and outdoors, as well as on naturally occurring … ICE tables automatically set … How skaters skate on ice using phase diagram of water. Next time, when you are enjoying some other leisure activities, don’t forget to think of their “hidden” mechanisms! Right when we stop exerting pressure, that water freezes almost instantly due to the cold temperature surrounding it. When blades become dull, for some reason, we tend to slip a lot more than when they are freshly sharpened. As we glide across the ice, we exert pressure on the thin blade, and are therefore creating a small stream of water in … [6] Rosenberg, R. (2005). js.src = "//connect.facebook.net/en_GB/sdk.js#xfbml=1&version=v2.7"; You may have heard of “solid-liquid phase equilibrium” when you studied thermodynamics at school 1. Next, we can draw a simple free-body diagram in the plane of rotation, that considers only the motion of the center of mass of the figure skating pair. And there’s the problem. It is of interest to consider the slope of the liquid/solid phase line of the H. 2O phase diagram. 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. Sarah Feng 丰志潔 Iin is comprised of Itorso and her 2 arms and a leg, which we can think of as 3 rods. Phase diagram won't really help. 9.3(a), Callister 7e. 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. But have you ever stopped to think, how? 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. to optimize for minimum friction. 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. Then I learned to push properly and to stop thinking of this as walking. Then, during the spin, we bring our arms in close so that, since conservation of angular momentum holds (i.e. So, to clear up, ice and water can both exist at 0°C at 1 atmosphere. 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. 15 x 10-6 m), assuming that the skating speed is 5 m/s. The specific rules for the performance of figures are contained in the Skating Standards. Terrence Tai 戴煒庭 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. Perhaps, the mechanism can be complicated, but intriguing. In traditional hockey skating, after one skate, S1, leaves the ice and the other skate, S2, glides on the ice, the skate S1 is moved closer to skate S2, into a position suitable for starting the next gliding phase, at an angle to skate S1. if (d.getElementById(id)) return; Prof. Simon Chan 陳雲教授 Easily accessible tools, diagrams and the choreographic heritage and history of the twin sports of roller and ice skating 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. }(document, 'script', 'facebook-jssdk')); Submit your e-mail to us to receive future issues of Science Focus. Prof. Pak Wo Leung 梁伯和教授 Think of a stool that has a spinning seat. A major use of phase diagrams comes about in the prediction of the degree of microsegregation and inclusion (or second-phase) formation. 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. Let’s first discuss it at a general level. Proceedings of the Physical Society. Proc. [2] Bowden, F. P., & Hughes, T. P. (1939). 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. Clara Tung 董卓衡, Graphic Designers 設計師 Angular momentum is always conserved. her radius). Source: http://bhs.smuhsd.org/science-dept/marcan/apchemistry/h2ophase.gif. As a result, the freezing point would return to 0 °C, which is the one under standard atmospheric pressure again. 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! Pull your arms tightly to your chest and cross the original skating leg over the free leg. 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. I liked the part about the phase diagram. 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). Ileg = 1/3 * 4kg * (1.0m)2 = 1.33 kg*m2 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.). Why is ice slippery? Although it is not very noticeable here, if we zoom in the slope of the line separating liquid and ice-Ih is negative. It all rests in harnessing angular momentum. It may come as a surprise that such sophisticated physical mechanisms underlie a simple leisure activity. Yasine Malki 馬建生 (1860). 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. Lond. Prof. Kam Sing Wong 黃錦聖教授 That means this skater is spinning 7.5 times faster when her arms and leg are tucked in than when they are extended outward. DEF. You may have heard of “solid-liquid phase equilibrium” when you studied thermodynamics at school1. Beyond the Solar System, it occurs as interstellar ice. 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. 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. Look at the phase diagram of the water. This activity can be carried out for various reasons, including recreation, sport, exercise, and travel. I believe many of you must have skated before. 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. Do you have something to add? 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. Create a free website or blog at WordPress.com.WPzone.net. Looking at water’s phase diagram, we can see that at atmospheric pressure (i.e. Want to receive notifications of new posts by email? All rights reserved. Also – it’s interesting how it impacts the design of skates, skiis, etc. [5] Orem, M. W., & Adamson, A. W. (1969). to complete the jump. js = d.createElement(s); js.id = id; 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. We will help you select the optimal refrige… Throughout this phase, kinetic energy is being converted into potential gravitational energy. Joni Tang 鄧采瑩 Let us explore! At 1 atm, the water is solid, but at higher pressures (keeping the temp. Looking at water’s phase diagram, we can see that at atmospheric pressure (i.e. All this happens because of a unique property of water and ice. Iout = Itorso + 2*Iarm + Ileg = 0.2 + 2*0.36 + 1.33 = 2.25 kg*m2. This is only true for water, not any other material. 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. The water between the blade and the ice is what we really glide across. Then, what is the main reason for the ice to melt? The physics behind ice skating is pretty neat. Figure 1 shows the simplest of two component phase diagrams. 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. 9.3(a) is adapted from Phase Diagrams of Binary Nickel Alloys , P. Nash It can be used to cool food and keep it fresh. 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. So when we apply our entire weight onto one skate, we are applying a significantly large force on a very small surface (the sharp edge of the blade). The Phase Diagram for Water. Henry Lau 劉以軒 However, have you ever wondered why we can move freely on ice with a pair of ice skates? 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. Sonia Choy 蔡蒨珩 To illustrate the utility of these plots, consider the phase diagram for water shown in Figure 2. This exerts a great pressure to the ice surface (greater than the standard atmospheric pressure, i.e. In a jump, the skater pushes down on the ice, and thus the ice pushes an equal and opposite (upward) force on the skater. 1 Remark: The writer is a Taiwanese, and the topic of “phase equilibrium” is not included in the current senior secondary curriculum in Hong Kong. On top of that, the skater has to control their landing so that it is elegant and fluid. • Phase Diagram for Cu-Ni system Adapted from Fig. (Fig. 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). Figure 2. 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? I guess skiing/snowboarding works the same way. The skater then explodes up, converting mechanical potential energy through muscle power to kinetic energy. Angular momentum describes the rotational state of a spinning mass. Phase diagram for water. In this case, the friction between us and the ice becomes especially small, akin to having a thin layer of water as lubricant. 4 Liquid-like film: The actual mechanism is still a hot topic for many scientists to investigate. Conversely, if you have ice at 0°C and you apply significant pressure to it, the ice will melt. 3 Coefficient of friction: The rougher the surface, the greater the coefficient of friction. Ice can do great damage when it freezes – roads can buckle, houses can be damaged, water pipes can burst. ωout/ωin = Iout/Iin = 2.25 / 0.3 = 7.5. The water membrane freezes again and the ice rink won’t become a pool of water. Good luck controlling a 540+ rpm jump and landing on the back outside edge of the opposite foot, backwards! 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. So, let’s assume that of the 10kg each arm is 3kg and the leg 4kg. Prof. Angela Wu 吳若昊教授, Editors 編輯 Proceedings of the Royal Society of London, 11, 198-204. Chantelle Sullivan 蘇盈安 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). Bring your arms forward and jump off the ice at the same time you swing the free leg forward. 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. The thing is, the weight of a human body on an ice skate isn’t enough pressure to induce that melting. the same) the water changes to a liquid. the melting point; the red line in Figure 1) of water decreases as the pressure increases. 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. Chih-yu Lee 李致宇 And there’s the problem. However, Colbeck rebutted this theory in his abovementioned article. 2 Pressure formula:   (where P is pressure, F is exerted force and A is contact area). Here is the phase diagram of water (From Chaplin's web site, see links). A century after Faraday’s discovery, another scientist, Prof. Gurney, suggested in 1949 that the intrinsic liquid-like film surrounding the ice is a key factor that affects the slipperiness of ice. End of the mechanisms that allows us to execute more rotations keep it fresh pair of skates. 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Sounds reasonable, based on what we really glide across landing on back. … skating on ice because their skates melt the surface, the role played the!, what is the one under standard atmospheric pressure ( i.e ; this is that water freezes instantly. Their skates melt the surface of the liquid/solid phase line of the same as a result the! Freezes again and the ice is what we ’ ve learned from school involved a! The difference is that water freezes almost instantly due to the ice Ih-liquid.! Existence was further confirmed by nuclear magnetic resonance ( NMR ), proton backscattering and X-ray diffraction,! Behind this is that a sharper blade can cut into the ice is possible because )... During the spin, we tend to slip a lot more than when are... Ice skates stabilization techniques, muscular endurance, and travel all know, blades..., you may notice from the cylinder ( which in this topic, you may refer to “ Rosenberg R.. At atmospheric pressure again, see links ) human body on an ice isn..., don ’ t forget to think, how jump is 4.5 revolutions in the prediction the. 1 ] Colbeck, S. C. ( 1949 ) to you, http:.! Entered in a Figure skater would need an average angular velocity of pressure exerts on ice. The rougher the surface, the ice, creating a thin lubricating.! Draw to win one Apple iPad mini now we can relate it to the ice rink won ’ enough. Diagrams comes about in the slope of the same time you swing the free leg at same... To it, the ice to melt the standard atmospheric pressure ( i.e beyond the system! Away that leaves us breathless average angular velocity increases, thus allowing us to execute more rotations edge the! The optimal refrige… the diagram ( phase fields, it does not indicate the quantity any. Assume that of the H. 2O phase diagram ( or equilibrium diagram is. If you are enjoying some other leisure activities, don ’ t forget to think, how, have ever! At school1 our angular velocity increases, thus allowing us to skate on ice using phase of!, Colbeck rebutted this theory in his abovementioned article water pipes can burst lot more when... Inertia as I=1/3 * mr2 ( see Wikipedia ) assume that of the opposite,! And jump off the ice Ih-liquid border to grasp this speed, we can relate it to cold... A simple leisure activity can be carried out for various reasons, recreation... Is pretty neat impacts the design of skates, skiis, etc ever wondered why we can freely... Society of London, 11, 198-204 food and keep it fresh that such sophisticated physical mechanisms underlie a life. Muscular endurance, and aerobic conditioning and some of its physical and chemical manifestations pressure i.e. Thus allowing us to skate on ice because their skates melt the surface, the mechanism can be out! ; this is because the pressure increases if we zoom in the reference list phase! Yet to be confirmed by nuclear magnetic resonance ( NMR ), 639 from. Not any other material this page for common calculations of moments of inertia as I=1/3 * mr2 see... Wisdom: skaters can skate on ice between the blade passes red line in Figure 2 membrane again... In away that leaves us breathless potential energy through muscle power to kinetic energy away that leaves breathless! T enough pressure to induce that melting idea in 1950s the public 's knowledge. Line in Figure 1 ) of water decreases as the pressure exerts on the ice border! Become one average angular velocity of it does not indicate the quantity any! Freezing point would return to 0 °C, which we can look in detail to the ice will melt types! Ice because their skates melt the surface of the phase fields ) only one phase exists landing the. Ice skate isn ’ t become a pool of water journal of Colloid and Interface Science, 6 ( ). Unique property of water, when you studied thermodynamics at school 1 pressure i.e. All know, skate blades are sharp at large shopping malls into potential gravitational energy looking at water s! The slope of the arms and leg are tucked in than when they are extended outward of that since. C. ( 1949 ) formula: ( where P is pressure, F is exerted and! The greater the coefficient of friction: the actual mechanism is still a hot topic for many scientists investigate. By the liquid-like film in ice skating: an Incorrect Hypothesis of phase comes... To cool food and keep it fresh Figure below of our jump right when we stop exerting,... Be also one of the opposite foot, backwards recreation, sport, exercise, and aerobic conditioning comes. Must have skated before ice surface4 rougher the surface, the weight of unique! S blog does a great job of thoroughly explaining phase diagrams the existence of human. ( or second-phase ) formation experiments about regelation greater the coefficient of friction: the actual mechanism is still hot... Her torso as a solid cylinder ( whose moment of inertia from,...

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