Gliding for Gold: The Physics of Winter Sports

5. Skiing—On the Slopes and on the Level

5 SKIING — ON THE SLOPES AND ON THE LEVEL There are many images from alpine skiing events at the 2010 Winter Olympics that stand out. You may recall Lindsey Vonn flying down the slopes at Whistler Creekside, bringing to that race a pedigree as world champion and a shin injury, and finishing the race with a gold medal— America’s first in women’s downhill. In the men’s 50-km cross-country event, Norway’s Petter Northug just beat Germany’s Axel Teichmann in a sprint finish to this grueling competition. These races took place in the coastal mountains above the city of Vancouver. Snow sports, unlike ice sports at the Olympics, necessarily take place outdoors. As a consequence , both track and meteorological conditions are much more variable . Weather a√ects snow properties, which a√ect track condition. Altitude influences both air resistance and athlete performance (the finish lines at Whistler Creekside, where all the 2010 alpine skiing events took place, are 2,700 feet above sea level). Despite this variability, we can still analyze alpine and cross-country skiing from a physics perspective and understand what is going on. The predictions we make will not be as accurate as for ice sports because of the unpredictability of conditions. For example, we must expect considerable di√erences in snow properties over a long-distance cross-country event, as the skiers pass from flatter to steeper terrain with humidity and shade variations, and variation in ambient temperature as the event progresses. Physics underlies everything, however, and in this chapter we apply it to alpine and cross-country skiing. G E T T I N G H I G H Many outdoor winter sports, such as skiing, take place at high latitudes or high altitudes to ensure a good covering of snow. Altitude influences performance significantly, for better and for worse, even for indoor sports. For example, in the 2010 Winter Olympic Games in Vancouver, no world records were set in long-track speed skating. (Only two Olympic records were set: Sven Kramer of the Netherlands in the 5,000-m event and Lee SeungHoon of South Korea at the 10,000-m event.) The reason is very clear. The facilities for the 2010 Games were excellent, but the skating track (the Richmond Olympic Oval) was at sea level. Similarly, no records were set during the Turin Winter Games in 2006. Turin is less than 800 feet above sea level. All men’s and women’s long-track speed skating world records, at all distances , have been set at altitude—mostly at Calgary (altitude 3,400 ft) or Salt Lake City (altitude 4,300 ft). The reason why altitude matters is, of course, because thin air at high altitude reduces aerodynamic drag. We saw in chapter 2 that for speed skaters, something like 80% of the power they expend during a race is used to overcome drag. Increased altitude reduces an athlete’s oxygen supply during a race; this, you might think, would make fast racing more difficult at highaltitude venues, but drag wins out: speed skaters who want to set world records do much better when high (up). The same argument applies to other racing events, such as downhill skiing, where speed is important. The influence of altitude upon race times is investigated in technical note 10, where I show that, especially for short races, rarefied air leads to faster races. The effects of altitude go beyond racing events, however. They influence all winter sports participants—not just downhill skiers or speed skaters. Athletes who normally compete near sea level have to make several adjustments when training for, and competing in, events at altitude. When training at altitude, they should increase the rest periods between exhaustive training sessions. It is a good idea for them, ahead of their competition event, to sleep and spend their free time at a higher altitude than the event venue. In competitions where it is permitted, athletes should supplement their oxygen intake on the sidelines or between events. In team sports such as hockey, substitutions should be made more often during games played at altitude. SKIING — ON THE SLOPES AND ON THE LEVEL 97 It isn’t just endurance that differs in the thin air of high-altitude competitions . Ski jumpers must adjust their lean angle, and there are similar technical adjustments necessary for downhill skiing and snowboarding. Athletes must take extra...