Hot or Cold: How Temperature Affects Sports

Fig2CrespoWe are always interested in knowing how hot or cold our day is going to be so we can plan for the day ahead of us. No matter what activities we plan, we want to accomplish them without unnecessary distress. Different ambient temperatures might encourage us to engage in outdoor activities, such as practicing sports, or postponing them for another time. Since any type of exercise produces heat as by-product, accumulation of too much heat in excessively high ambient temperatures can compromise athletic performance. This detriment to athletic performance can also arise when ambient temperatures are excessively low. Our bodies cope with changes in temperature through different thermoregulatory processes. However, without taking proper precautions prior to and after exercising, this regulation of body temperature might not be enough, and cannot only make us feel uncomfortable, but also put our health at risk.

Learn the basics of temperature and sports or read the more technical explanation.

Articles by Jose G. Crespo.

Hot or Cold: How Temperature Affects Sports (Technical)

Fig1Crespo

Fig. 1. Organization of vertebrate skeletal muscles (From ref. 1).

Like other tissues, skeletal muscle tissue consists of cells (muscle fibers). The size of these cells ranges from 5 to 100 μm in diameter, and they are up to several centimeters long (Randall et al. 2002). Their parallel arrangement allows for the fibers in a muscle to pull together in a specific direction to exert force. This muscle force is achieved by parallel subunits inside muscle fibers (myofibrils) which in turn consist of sarcomeres, the longitudinally repeated functional units of muscle. The importance of the sarcomere is that its arrangement helps us understand the molecular basis for muscle function. Each sarcomere contains two proteins arranged in a particular geometric pattern, namely actin and myosin, and the interaction between these two proteins explains how a muscle is able to contract (current mechanism known as the sliding-filament theory; see Fig. 1). This contraction requires energy and it is obtained from glucose and lipids that are in turn transformed into adenosine triphosphate (ATP), the energy currency of the cell. Both ATP production (see how chemistry fuels running) and hydrolysis release heat, and it is this heat that contributes to the body’s temperature.

ATP is necessary for muscle work because of two major processes that are energy-dependent. The first process has to do with the cycling of attachment and detachment of myosin cross-bridges to actin, which is mediated by an enzyme called actomyosin ATPase. Without ATP, the myosin heads cannot detach from the actin filament for a new cycle. The second process involves the pumping of Ca2+ (calcium ions) back into the sarcoplasmic reticulum of the muscle fiber by an enzyme called sarcoplamic reticulum ATPase. Free Ca2+ induces muscle contraction by binding to troponin (a muscle protein) which changes the configuration of another protein, tropomyosin, allowing for the myosin heads to access myosin binding sites on the actin filament. During strenuous exercise, muscle energy consumption can surpass that of a resting muscle 100-fold and achieve rates of energy consumption greater than 1.5 kg ATP per minute of activity (McIntosh et al. 2006). If we reflect on the facts that skeletal muscle constitutes about 40% of our total body weight and that muscle contraction is only ~25% efficient, we immediately realize that a lot of expended energy must be released as heat (Sawka and Young 2006). In fact, about 3 joules of energy are released as heat for every joule of chemical energy that is converted into mechanical work4. This extra heat produced during activity is added to the heat generated by our basal metabolism and increases body temperature (2-4°C increase in core temperature is common after strenuous exercise; Randall et al. 2002). Excessively high body temperatures threaten enzymatic activity and thus, avoiding excessive heat storage is of paramount importance when exercising.

Athletes performing different types of exercise rely on the strength of specific muscles. This strength depends on muscle morphology and architecture and myosin isoform composition (see genetic aspects in How Much do Genes Affect Your Athletic Potential?). The phenotypic profiles of muscle fibers cannot only be affected by neuromuscular activity, hormones and aging, but also by the athletic training a person undergoes. Broadly speaking we can define two types of exercise: high-resistance exercise and endurance exercise. The first one results in greater muscle mass and strength by involving some form of high-intensity weightlifting for a short duration (8-12 repetitions) two to three days a week. In contrast, muscular endurance is achieved by low-intensity exercise regimes during 30-60 minutes on an almost daily basis (McCarthy and Esser 2012). Thus, athletes usually bear this in mind when exercising. But, irrespective of the type of exercise, we always feel an increase in body temperature associated with activity. How is it then that our body copes with the excess heat generated during sports or other physically-demanding activities?

Metabolic heat generated by active muscles is transferred to the bloodstream and then to the body core. Whether this heat increases our body temperature or not will depend on different environmental variables, particularly ambient temperature. For example, in cold climates we can suffer from heat loss, which will lower our body temperature and cause our metabolic rate to slow down. If body heat generation cannot keep up with the dissipation of heat to the environment, our body temperature will eventually decrease to dangerous low levels, and may even end in death. The opposite can happen in hot climates. If we cannot dissipate enough heat, we accumulate heat causing our metabolic rate to increase (which generates even more heat) and leads to overheating. This can also end in death. Fortunately, since most of us do not experience extreme weather on a regular basis, our bodies are able to handle this interplay between internal and external temperature in different ways.

Fig2Crespo

Fig. 2. Avenues of heat exchange for an athlete performing exercise in air (From ref. 3).

Humans can be classified as endotherms, which means that our own energy metabolism produces the heat that determines our body temperature. Endothermy allows us to also be homeotherms, because our body temperature is relatively constant and independent of ambient temperature (core body temperature in humans is about 37°C). Thermoregulation in homeotherms occurs through two collaborative processes, namely behavioral and physiological temperature regulation. The first consists of conscious and unconscious behavioral changes influencing heat storage, like modifying activity levels, seeking shade or sunlight, reducing surface area for heat exchange and even changing clothes. Physiological temperature regulation encompasses responses that are unconscious. Our bodies can control the rate of metabolic heat we produce (e.g., by shivering), as well as heat loss by sweating and blood flow distribution (e.g., cutaneous vasodilatation and vasoconstriction). This last mechanism facilitates heat transfer from the skin to the surrounding air or water and is highly dependent on environmental temperature, air humidity, air or water motion, radiation and clothing (Gavin 2003). Biophysically speaking, this heat transfer can be achieved by non-evaporative avenues (conduction, convection, and radiation) called “dry heat exchange” or via evaporative cooling (see Fig. 2). Evaporation is induced by sweating (it can begin after just 2 seconds of engaging in heavy physical work; Randall et al. 2002) when we exercise, and it is the only known mechanism for dissipating heat against a thermal gradient. For example, on a hot day in the desert, our exocrine glands can produce over 12 liters of sweat, effectively cooling our bodies to tolerable temperatures (Jablonski 2006). However, the effectiveness of sweating is low in very humid environments, making it extremely difficult to get rid of excess heat.

Usually our motivation to win or complete a certain task leads us to ignore effective thermoregulatory strategies, and this usually causes lower performance, injuries and/or heat related illnesses. On top of thermoregulatory strategies during activity, there are also several pre- and post-exercise strategies that aid us in performing better and avoiding injuries (Noonan et al. 2012, Ross et al. 2013, Very et al. 2013). For example, warming up and stretching prior to exercising has been shown to deter muscular injuries. In general, warm-up is defined as activities that make us sweat mildly but do not fatigue us, with the purpose of improving muscle dynamics and preparing us for more stringent demands of subsequent exercise. There are two types of warm-up, active and passive. Active warm-up is the most common type of warm-up for both amateur and professional athletes and involves some kind of non-specific body movement (e.g., jogging, cycling or callisthenics). In contrast, passive warm-up results from the increase of muscle temperature or core body temperature by external means, like heating pads, vibrational devices (Cochran 2013), hot showers, saunas, etc. Stretching, as part of warm-up, is recommended within 15 minutes prior to activity to obtain the best results (Woods et al. 2007). Post-exercise strategies are more commonly used by professional athletes after very demanding activities that may lead to muscular fatigue and injuries. These usually involve some kind of muscle cooling technique (DeGroot 2013). Finally, every athlete knows that good nutrition (see Putting Protein in Its Place)  and hydration (see Hydration and Sports Beverages) are essential for safe and effective exercising. In particular, hydration is strongly linked to thermoregulation. Although sweating allows us to get rid of excessive heat efficiently, it also presents the risk of dehydration, if not enough water is consumed.

Regular physical activity enhances and maintains health, but we need to take special considerations (like the ones we saw above) when engaging in sports or other vigorous physical activities. This is particularly true in hot and humid weather, which cannot only lead to poor athletic performance but also to heat stress and even death. Besides inadequate hydration, excessive heat retention can be caused by physical exertion, insufficient recovery time in-between activities, and inappropriate clothing. Heat stress can come in the form of heat cramps (painful cramps in abdominal muscles and muscles of the extremities), heat syncopes (weakness, fatigue and fainting), heat exhaustion due to water and/or salt depletion (causing exhaustion, muscle cramps, nausea, vomiting, dizziness, elevated temperature, weakness headaches, etc.), and heat strokes due to failing thermoregulation (causing nausea, seizures, disorientation, and in severe cases unconsciousness or comatosis). There are also serious risks associated with exercising in cold weather (Castellani and Young 2012). For example, sprains and strains are common, and in very cold-weather, frostbite and hypothermia (core body temperature dropping below that required for normal metabolism) can present a challenge to unprepared athletes.

All of these health related issues can be avoided by learning on the one hand, about the different strategies that our bodies use to control body temperature and, on the other hand, ways of helping our bodies to thermoregulate when external conditions are too harsh. We should always reduce the risks of heat-related illness, by hydrating and eating appropriately, adjusting exercise activity levels according to our current fitness status, having adequate recovery periods between bouts of exercises, and realizing when it is better to cancel athletics and stay home (Heat-Related Illnesses 2014).

By Jose G. Crespo
Jose G. Crespo is a researcher in the field of animal physiology and behavior with an emphasis on insect thermoregulation and neuroscience. He is currently a Postdoctoral researcher at the University of Utah – Department of Biology.

References

Castellani, J. W., & A. J. Young. 2012. Health and performance challenges during sports training and competition in cold weather. British Journal of Sports Medicine. 46: 1-5.

Cochrane, D. 2013. The sports performance application of vibration exercise for warm-up, flexibility and sprint speed. European Journal of Sport Science. 13: 256-271.

DeGroot, D. W., R. P. Gallimore, S. M. Thompson, & R. W. Kenefick. 2013. Extremity cooling for heat stress mitigation in military and occupational settings. Journal of Thermal Biology.   38: 305-310.

Gavin, T, P. 2003. Clothing and thermoregulation during exercise. Sports Medicine. 33: 941-947.

Heat-Related Illnesses (Heat Cramps, Heat Exhaustion, Heat Stroke). University of Utah Health Care, n.d. Web. 1 April 2014. Available at: https://healthcare.utah.edu/healthlibrary/centers/ortho/doc.php?type=90&id=P01611

Jablonski, N.G. 2006. Sweat. In Skin: A Natural History, pp. 39-55. Berkley: University of California Press.

MacIntosh, B. R., P. F. Gardiner, & A. J. McComas. 2006. Muscle Metabolism. In Skeletal Muscle: Form and Function (2nd Ed.), pp. 209-223. Chelsea, MI: Sheridan Books.

McCarthy, J. J., & K. A. Esser. 2012. Skeletal Muscle Adaptation to Exercise. In Muscle: Fundamental Biology and Mechanisms of Disease (ed. J.A. Hill & E.N. Olson), pp. 911-        920. San Diego: Elsevier.

Noonan, B., R. W. Bancroft, J. S. Dines, & A. Bedi. 2012. Heat- and Cold-induced Injuries in Athletes: Evaluation and Management. Journal of the American Academy of Orthopaedic Surgeons. 20: 744-754.

Randall, D., W. Burggren, & K. French. 2002. Energetic Costs of Meeting Environmental Challenges. In Animal physiology: Mechanisms and adaptations (5th Ed.), pp. 699-736. New York: W. H. Freeman.

Randall, D., W. Burggren, & K. French. 2002. Muscles and Animal Movement. In Animal physiology: Mechanisms and adaptations (5th Ed.), pp. 361-424. New York: W. H. Freeman.

Ross, M., C. Abbiss, P. Laursen, D. Martin, & L. Burke. 2013. Precooling methods and their effects on athletic performance: a systematic review and practical applications. Sports Medicine. 43: 207-225.

Sawka, M. N., & A. J. Young. 2006. Physiological Systems and Their Responses to Conditions of Heat and Cold. In ACSM’s Advanced Exercise Physiology (ed. C.M. Tipton),    pp. 535-563. Baltimore: Lippincott Williams & Wilkins.

Versey, N. G., S. L. Halson, & B. T. Dawson. 2013. Water immersion recovery for athletes: effect on exercise performance and practical recommendations. Sports Medicine. 43:       1101-1130.

Woods, K., P. Bishop, & E. Jones. 2007. Warm-up and Stretching in the Prevention of Muscular Injury. Sports Medicine. 37: 1089-1099.

Hot or Cold: How Temperature Affects Sports (Basic)

Fig2CrespoWe wonder whether the day ahead of us is going to be hot or cold in order to decide if we should do certain activities, like practice our favorite outdoor sports. We might think that no matter how hot or cold it gets, we should still go on our running routine because exercise is always good for us. However, we should always remind ourselves that excessive heat or cold can not only make us uncomfortable during exercise, but even put our health at risk.

Based on morphological characteristics, muscles can be classified into two major types, smooth muscle (e.g., the type of muscle found in the walls of hollow organs such as blood vessels) and striated muscle (including heart muscle and skeletal muscle). Skeletal muscles generate most of the heat that causes body temperature to rise during exercise, and thus, it is the main focus of this article.

Muscle contraction requires energy. In muscle cells, like in any other cells, adenosine triphosphate (ATP) is the molecule that stores energy. This energy is transformed into work by the muscles that we use during a specific activity. However, not all the energy is transformed into work. Both the production and hydrolysis (water-mediated cleavage of chemical bonds) of ATP release heat as a by-product, and it is this heat that contributes to the body’s temperature.

Since we are homeotherms (our body temperature is kept relatively constant with respect to ambient temperature), our basal metabolism is higher than that of non-homeotherm animals. When we engage in any type of activity, our body produces extra heat that is added to the heat generated by our basal metabolism and thus, our body temperature increases. If our bodies could not regulate internal temperature, we would store great amounts of heat compromising cell function.

We can regulate body temperature via behavioral and physiological means. For example, we can exercise in the shade to avoid direct sunlight (behavioral) and depending on ambient temperature, we can experience vasodilation (widening of blood vessels) and vasoconstriction (narrowing of blood vessels) to facilitate or restrict heat transfer from the skin to the surrounding air. Thus, thermoregulation can profoundly affect how we perform in different sports and under different ambient conditions.

Furthermore, we need to be extra careful when engaging in sports or other vigorous physical activities in hot and humid weather. Hot weather means that we may accumulate heat more rapidly than what our body can dissipate, and humid conditions imply that sweating (the only known mechanism for dissipating heat against a thermal gradient) may not be possible. Under these circumstances we are prone to suffer from heat stress. Heat stress can lead to cramps, syncopes, exhaustion, and even stroke.

All of these can be avoided by learning about the different strategies to reduce the risks of heat-illness, always hydrating appropriately, adjusting exercise activity levels according to current fitness status, having adequate recovery periods between bouts of exercise, and realizing when it is better to cancel athletics and stay home.

Read the technical details about body temperature and sport.

By Jose G. Crespo
Jose G. Crespo is a researcher in the field of animal physiology and behavior with an emphasis on insect thermoregulation and neuroscience. He is currently a Postdoctoral researcher at the University of Utah – Department of Biology.

Curling: The Friction Sport

pic_curlingCurling was first created in 16th century Scotland, where river bottom rocks were slid across ice-covered lochs to a target. In modern times, the “roaring game,” named for the sound of the “stone” sliding across the ice, is more refined. It consists of a 41 pound granite stone sliding across 42 m of ice to a target called a house, utilizing pebbled ice rinks, brooms, curling shoes, and carefully formed stones.

The ice rinks used for Curling are not smooth, but have a pebbled surface made by spraying the rink with water and allowing the tiny droplets to freeze on its surface. This surface is necessary for the stone to have suction and slide across the ice. Two players with “brooms” vigorously sweep the ice immediately in front of the stone to influence the trajectory, or direction it travels. These players wear a “gripping” shoe and a “sliding shoe,” which allow them to use friction to move along the ice. As the stone travels, the interaction between the stone, ice, and sweeping changes the sources of friction, and cause the stone to “curl” in a curved trajectory, giving the sport its name.

Although there are many theories, it is poorly understood as to what causes the stone to curl as it travels along the ice. As the sport gains popularity, further scientific inquiry can be expected to explore the role of friction and different sweeping styles.

Learn the basics or read about the technical aspects of friction in curling.

Articles by Jessica Egan

Curling: The Friction Sport (Basic)

The modern game of curling consists of a 41 pound granite rock sliding across some 42 m of ice to a target called a house. The rock, technically termed a “stone,” is typically preceded on the ice by two players with “brooms,” who vigorously sweep the ice immediately in front of the stone to influence its trajectory (Willoughby et al. 2005, Bradley 2009, Esser 2011). This unique winter sport, affectionately termed the “roaring game” because of the sound the stone makes as it slides on the ice, has its roots in 16th century Scotland, where river bottom rocks were the stones which slid across ice-covered lochs to a target (Clark 2008). Now, play is more refined, utilizing pebbled ice rinks, brooms, curling shoes, and carefully formed granite stones.

The ice rinks are pebbled by spraying water onto the ice to make a slightly bumpy surface as the droplets freeze into little protrusions on the ice surface, without which the stone could not curl (Shegelski 2001). Brooms are now typically made of synthetic materials such as nylon, and curling shoes consist of one shoe with a larger friction coefficient than the ice and another shoe which has a friction coefficient smaller than that of the ice, thus providing players with a “gripping” shoe on one foot and a “sliding shoe” on the other. A friction coefficient is the measure of how much a substance resists sliding on another substance. The granite stones are highly polished, very hydrophobic, and have a small hollow on their underside so that only a small ring on the bottom of the stone actually touches the ice at any one time.

Each of the pieces of equipment needed to play curling is designed to maximize the impact it has on friction coefficients. Style of play also influences friction coefficients. For example, some sweepers use a conventional style of sweeping, which consists of the sweeper standing to the side of the stone while they sweep. The sweepers employ more force closest to their feet, so there is a greater rise in temperature on the side of the stone closest to the sweeper, which causes asymmetric friction acting on the stone. This matters because the sweeping causes the uppermost layer of ice to melt, thus providing a lubrication layer for the stone to glide on. On the other hand, a high-angle style of sweeping consists of the sweepers being behind the stone while it travels, giving a more even distribution of heated ice, and so lessening the curl of the stone (Marmo 2006). Both can be useful, depending on where the stone is desired to go.

There is much scientific debate about the role friction plays in causing the stone to curl. The friction acting on the stone is undoubtedly asymmetric, but how this results in the stone’s curling trajectory is not yet fully understood. Some believe that as the stone twists, it pushes the water layer to the side, creating a lubrication film for the rock to slide on (Bradley 2009). Others say that the rotating stone not only pools water one its one side, but also chipped ice and other debris (Denny 2002). As curling continues to gain popularity, it can be expected that further scientific inquiry will continue to be directed at exploring the role of friction in the curl of the stone.

Learn more about the technical aspects of friction and curling.

By: Jessica Egan, University of Utah
Jessica Egan began her love of chemistry under her mom’s direction with homeschool experiments in middle school and then up into high school through her high school chemistry teacher. She pursued a chemistry and art double major at Hillsdale College and decided to continue her chemical education by attending graduate school at the U. She has recently graduated with a M.S. from the U in Analytical Chemistry and is looking for a career in industry.

References

Bradley, J. L. 2009. The sports science of curling: a practical review. Journal of Sports Science and Medicine 8:495-500.

Clark, D. 2008. The roaring game: a sweeping saga of curling. Key Porter Books, Toronto, Ontario, Canada.
Denny, M. Curling rock dynamics: towards a realistic model. 2002. Canadian Journal of Physics 80:1005-1014.

Esser, L. 2011. Swept away: exploring the physics of curling. Science Scope 35:36-39.

Marmo, A. A., I. S. Farrow, M-P Buckingham, and J. R. Blackford. 2006. Frictional heat generated by sweeping in curling and its effects on ice friction. Proceedings of the Institution of Mechanical Engineers, Part L.: Journal of materials: Design and Applications 220:189-197.

Marmo, B. A., M-P Buckingham, and J. R. Blackford. 2006. Optimising sweeping techniques for Olympic curlers. The Engineering of Sport 6 3:249-254.

Shegelski, M. R. A. 2001. Maximizing the lateral motion of a curling rock. Canadian Journal of Physics 79:1117-1120.

Willoughby, K. A., and K. J. Kostuk. 2005. An analysis of strategic decision in the sport of curling. Decision Analysis 2: 58-63.

Curling: The Friction Sport (Technical)

The modern game of curling consists of a 41 pound granite rock sliding across some 42 m of ice to a target called a house. The rock, technically termed a “stone,” is typically preceded on the ice by two players with “brooms,” who vigorously sweep the ice immediately in front of the stone to influence its trajectory (Willoughby et al. 2005, Bradley 2009, Esser 2011). This unique winter sport, affectionately termed the “roaring game” because of the sound the stone makes as it slides on the ice, has its roots in 16th century Scotland, where river bottom rocks were the stones which slid across ice-covered lochs to a target (Clark 2008). Since its revival in the mid-1800s in Scotland, curling has somewhat switched continents with Canada now being the world’s main curling powerhouse. Curling has grown to an Olympic sport and enjoys a unique niche of fans and followers (Holt 1989, Tranter 1989).

From the view of science, curling is a game about friction. The friction of the stone on the ice, the brooms on the ice rink, and even the footwear of the curlers on the ice, makes the game possible. Curlers wear a sliding shoe, which has a lower friction coefficient than the ice, and a non-sliding shoe, which has a friction coefficient larger than that of ice, giving the players the ability to step and slide (Dassler 1986). The sweeping of the brooms varies the friction coefficient of the ice, making it possible to influence the trajectory of the stone once it has already been pushed toward the house. A covering for the handle of the brooms has even been proposed, to lessen the friction (and thus wear) of the broom on the curlers’ clothing, a long recognized problem for curlers (Robertson 1987). The entire game centers on creating and decreasing friction to one’s advantage.

In order to understand the science behind the sport, a more thorough description of the physical characteristics of the rink and the stone is needed. First of all, the ice on the curling rink is not polished and smooth. Rather, it has a pebbled surface made by spraying the rink with water and allowing the tiny droplets to freeze on its surface. The pebbled surface is critical to the game. As for the stone, which is made of a very hydrophobic granite traditionally from northern Wales or the island of Ailsa Craig in Scotland, its under-surface is not flat either. Instead, it is slightly hollowed out, making room for a small air pocket and causing only a thin annulus around the bottom to make contact with the rink. Coupled with the fact that the ice rink is pebbled, the annulus actually only touches a few of the little pebble protrusions on the ice, making its true contact with the ice very low indeed (Shegelski 2001). The pebbled surface and the stone’s small hollow also do away with the potential problem of liquid getting trapped under the stone and suctioning it to the rink surface.

There has been much debate among scientists about how the different sources of friction influence the game. Of particular interest is the three-way interaction between the stone, the ice, and the sweeping of the brooms and how the interaction of all three causes the stone to “curl,” i.e. have a trajectory which curves, giving the sport its name. This mysterious curling motion has received a lot of attention, although a complete understanding of the motion is still lacking. To begin to understand the curling motion, one must first understand the physics of how the stone glides across the ice. One thought is that as the stone slides along the ice, the vigorous broom sweeping directly in front of the stone causes the ice temperature to raise just enough to create a thin lubrication layer of water from the melted ice, reducing the coefficient of friction that the stone is traveling over (Marmo et al. 2006). Another viewpoint, however, points out that there cannot possibly be a lubrication layer of water supporting the stone because the stone rests on a pebbled, not a flat, surface (Denny 2002). The lubrication layer would simply never accumulate because the liquid would spread out between the small pebbled ice protrusions that the stone rests on. On the other hand, since the stone rests on a pebbled surface, each individual protrusion receives more pressure from the stone, thus melting the ice on the surface of the protrusions and creating a lubricating layer even more easily (Shegelski et al. 1999). Regardless of the mechanism, it is clear that the friction coefficient of the ice does change with sweeping, and the pebbled surface also influences curling. Studies have shown that on a smooth ice surface, little to no curling occurs. On a dry surface, the friction coefficient is constant, but the effects of a stone on such a surface cause it to behave in the opposite way than on ice (Jensen et al. 2004).

 

Friction


So why does the stone actually curl? It has been suggested that it may be because of an asymmetrical buildup of friction. If, for example, a stone is sent forward with a slight clockwise twist, any debris on the ice will be pushed to the right side of the stone. Any liquid layer that forms from the pressure and friction will also push the water to that right side of the stone, slightly pooling the water on one side. This means that on the right and front side of the stone, there is more lubrication from the melted ice, so the stone as a whole experiences an asymmetric coefficient of friction (Bradley 2009). Additionally, if a sweeper stands to the side of the advancing stone to sweep, more heat is generated in the part of the sweeping stroke that is closest to the sweeper, so the ice will have a larger decrease in the friction coefficient on that one side of the stone (Marmo 2006). Additionally, if the stone moves too slowly, it may actually increase the coefficient of friction because as the heavy stone slides across the pebbled surface, its pressure and heat of movement causes the small ice pebbles to break off, leaving small pebbles to grate underneath the advancing stone (Denny 2002).

Despite these theories, one model concludes that no matter how the coefficient of friction is changed and distributed across the different sides of the stone, the real motion of a curling stone remains entirely unaccounted for compared to the models (Nyberg et al. 2012).

How one sweeps also affects the way the ice melts. Sweeping plays a large role in the game by simply raising the temperature of the ice so that the friction coefficient decreases and with the raised temperature, it will be all the easier to melt the ice once the stone hits where the brooms have just swept. As the ice is brought closer to its melting temperature, the energy it takes to completely melt it decreases (Marmo et al. 2006). Next comes a question as to whether one ought to sweep harder or faster, with a low angle with respect to the ice or with a high angle. And does sweeping play a larger role in altering the friction coefficient by polishing the ice, or is its chief role to melt the ice? Since the ice is orders of magnitude smoother than the stone, any polishing done to the ice has a negligible effect, although sweeping aside any debris is useful, and we see that the key use of sweeping is how it raises the temperature (Marmo 2006). We thus see that the key use of sweeping is how it raises the temperature of the ice.

Even the styles of sweeping also make a difference in the amount of friction present in the game  – sweepers may use the conventional style, which consists of sweeping in front of the stone while standing to the side, or a high-angle style in which the sweeper standing behind the stone reaches over the stone to sweep in front of it. The high-angle style produces a stroke that overlaps each preceding stroke, giving a thermal history of ice at a more elevated temperature. The friction coefficient is thus lowered since each patch of ice is swept (and heated) several times. This is a clear advantage of this style – however, the drawback is that the high-angle style is farther away from the stone than the conventional style, meaning that although the ice experiences a greater increase in temperature when utilizing the high-angle style, the ice has a longer time to cool back to freezing before the stone reaches it, unlike the conventional style (Marmo 2006). There is also the question of whether it is better to sweep faster or harder. Sweeping twice as hard produces twice as much heat (Bradley 2009) which is desired in some instances, but in others, it is more advantageous to sweep faster so that the strokes can overlap each other and warm the ice more in that way. Regardless, when sweeping is done at the proper moment with the right technique, the power of friction can be leveraged to add 20-30 feet to the distance a stone can travel (MacDonald 1996).

The competing sources of friction and more particularly, the various means to alter friction coefficients during the game, give curling its unique qualities and intriguing scientific questions. As curling continues to gain popularity, it can be expected that further scientific inquiry will continue to be directed at exploring the role of friction in the curl of the stone, until it can be answered with certainty how the asymmetric friction coefficients acting on the stone cause it to curl.

 

By: Jessica Egan, University of Utah
Jessica Egan began her love of chemistry under her mom’s direction with homeschool experiments in middle school and then up into high school through her high school chemistry teacher. She pursued a chemistry and art double major at Hillsdale College and decided to continue her chemical education by attending graduate school at the U. She has recently graduated with a M.S. from the U in Analytical Chemistry and is looking for a career in industry.

 

References 

Bradley, J. L. 2009. The sports science of curling: a practical review. Journal of Sports Science and Medicine 8:495-500.

Clark, D. 2008. The roaring game: a sweeping saga of curling. Key Porter Books, Toronto, Ontario, Canada.

Dassler, A. A. 1986. Pair of shoes for the sport of curling. Patent Number 4,578,883.

Denny, M. 2002. Curling rock dynamics: towards a realistic model. Canadian Journal of Physics 80:1005-1014.

Esser, L. 2011. Swept away: exploring the physics of curling. Science Scope 35:36-39.

Holt, R. 1989. Sport and the British: a modern history. Oxford University Press, Oxford, U.K.

Jensen, E. T., and M. R. A. Shegelski. 2004. The motion of curling rocks: experimental investigation and semi-phenomenological description. Canadian Journal of Physics 82:791-809.

MacDonald, J. A. 1996. Artificial curling rink. Patent Number 5,566,938.

Marmo, A. A., I. S. Farrow, M-P Buckingham, and J. R. Blackford. 2006. Frictional heat generated by sweeping in curling and its effects on ice friction. Proceedings of the Institution of Mechanical Engineers, Part L.: Journal of materials: Design and Applications 220:189-197.

Marmo, B. A., M-P Buckingham, and J. R. Blackford. 2006. Optimising sweeping techniques for Olympic curlers. The Engineering of Sport 6 3:249-254.

Nyberg, H., S. Hogmark, and S. Jacobson. 2012. Calculated trajectories of curling stones sliding under asymmetrical friction. Conference Paper from the 16th Nordic Symposium on Tribology 12-15.

Robertson, C. M. Curling brooms. 1987. Patent Number 4,638, 522.

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Shegelski, M. R. A., R. Niebergall, and M. A. Walton. 1996. The motion of a curling rock. Canadian Journal of Physics 74:663-670.

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