The science of winter sports

Guest post by Dr. Mark Denny

Sports science is an expanding industry, judging by the number of scholarly journals out there that are dedicated to one aspect or another of sports. I get emails inviting me to contribute to this or that journal, or to attend specialist conferences on specific topics within the field (sports injuries, sports development, sports economics . . . ). These journals and conferences deal with all kinds of complicated technical matters, including team psychology, optimum tactics for team sports, baseball bat design, soccer scoring statistics, and so on.

In the context of winter sports, you can find articles written about superior ski wax, best bobsled designs (satisfying the very strict criteria set down in the rules of international bobsled), ski jump design, etc. From the point of view of a physicist like me, however, the complexity of winter sports science is confined to detailed technological subjects (think ski wax—an arcane, detailed technical subject if ever there was one). This complexity does not extend to what most viewers of the Winter Olympics would consider to be the crucial factor: the movement of athletes. It is a perhaps-surprising fact that, unlike summer sports, the physics of athlete movement in winter sports is actually quite simple.

Well, relatively simple. There are three basic forces that dominate the movement of athletes: the force of gravity acting down; aerodynamic drag, which acts opposite to the direction in which the athlete is heading; and, in many sports, the centrifugal force that acts on athletes, such as bobsledders, who are moving around a curve. When it comes to winter sports, all three of these forces take a quite simple form. The friction that a skate blade moving over ice is subjected to is well understood, physically. The friction of snow against ski is trickier, because snow is more varied in its nature and it deforms a lot. The curvature of bobsled tracks is well defined, so that the centrifugal force that acts on a sled and its crew careening round a bend is easy to determine.

In addition to these three basic forces, there are internal forces that act, as when a skier tucks in to reduce drag, or angulates to maneuver past a pole. Such internal forces are difficult to describe in detail, but if we are interested in only the overall movement of the athlete—where the skier is on the hill, not how she adjusts her stance at any given moment—then the science simplifies a lot, and we can make predictions (for example, about how long it will take a skier to descend a slope) quite accurately.

So how does the knowledge of sports science in general, and sports physics in particular, affect a scientist’s appreciation of a winter sporting event? Some folk would have you believe that reducing the performance of an Olympic athlete to numbers somehow diminishes their achievements, and that, by number-crunching a competitive event, we scientists are missing the beauty of movement or the thrill of the chase. Don’t you believe it.

Here is just one example. Cross-country skiers struggling uphill may seem, to an armchair viewer, to indulge in a lot of uncoordinated effort that makes them resemble drunken octopuses on caffeine. Analyze the movements of these athletes, however, and you see that they couldn’t be more efficient. Once you understand how much power these skiers are exerting, and realize that they exert that power for such extended periods, you’ll  hardly be surprised that, in past Winter Olympics, cross-country skiers have collapsed over the finish line.

The sledding sports at Sochi—bobsled, luge, and skeleton—are the simplest for sports scientists to analyze because they involve rigid structures moving over ice. As a direct consequence, the difference between a gold medal and no medal is miniscule—perhaps a hundredth of a second. Science has determined the best sled shape, athlete position, etc., before the start of a race. After that, physics takes over.

ski tracks 2

Denny comp.inddMark Denny is a theoretical physicist who worked in academia and industry. He is the author of a number of popular science books, most recently Lights On! The Science of Power Generation. Denny also wrote Gliding for Gold: The Physics of Winter Sports and The Science of Navigation: From Dead Reckoning to GPS, both published by Johns Hopkins.

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