Tag: Winter Olympics

Beijing 2022: Sliding on Snow
Skiing and snowboarding events rely on the peculiar physics of sliding on snow. According to classical lubrication theory, that sliding shouldn’t be nearly as low in friction as what we observe. The key here is that snow is soft and porous; it’s compressible, but it can also trap air (or water) in the pores between flakes. Because the passage of a skier or snowboarder is so fast, the air doesn’t have the time to slip out of the pores. Instead, it gets pressurized, providing lift that keeps the slider’s friction low. In the end, it isn’t the snow holding the slider up, it’s the air trapped in the snow beneath them! (Image credit: skier in powder – J. Andersson, snowboarder – Visit Almaty, halfpipe – P. T’Kindt; research credit: Z. Zhu et al.)
February 11, 2022
Beijing 2022: Ice’s Slideability
As scientists continue to unravel the peculiarities of ice, they’ve found that ice’s friction depends both on the object sliding on it and the ice’s hardness. At extremely low temperatures, water molecules at the ice’s surface are held rigidly by the hard ice, resulting in high friction. At intermediate temperatures, however, water molecules at the surface were more mobile — especially with a quick-moving slider going by — so the friction decreased.
But as the ice approached its melting point, the friction behavior shifted again. As the ice softened, sliding objects could begin to plough into the ice, dramatically increasing contact and friction. When ploughing begins depends on temperature, slider shape, contact pressure, slider speed, and ice hardness.
Beyond the lab, researchers found that weather plays a role in slideability, too, since humidity and air temperature can affect the thickness of the liquid-layer at the ice’s surface. (Image credit: SHVETS Productions; research credit: R. Liefferink et al.; via APS Physics; submitted by Kam-Yung Soh)
February 10, 2022
Beijing 2022: Monobob
Bobsleigh, as a discipline, has been dominated in recent years by teams seeking every aerodynamic advantage to shave hundredths of a second off their runs. So it’s fascinating that the newest event in the discipline — the women-only monobob — cuts away that secretive part of the sport by permitting sleds from only one manufacturer. Every athlete competes in an identical sled. Not only that, they swap sleds between runs based on their times! So the fastest athlete from the first run will switch sleds with whomever had the slowest time.
The event’s rules refocus the competition on athletic performance and skill rather than incentivizing countries who can afford to spend more money on wind tunnel testing and F1 design companies. That’s a great step toward leveling the playing field. I can’t wait to watch! (Image credit: OIS)
February 9, 2022
Beijing 2022: Ski Jumping
In ski jumping, aerodynamics are paramount. Each jump consists of four segments: the in-run, take-off, flight, and landing. Of these, aerodynamics dominates in the in-run — where jumpers streamline themselves to minimize drag and maximize their take-off speed — and in flight. During flight, ski jumpers spread their skis in a V-shape and lift their arms to the sides to turn themselves into a glider. Their goal is to maximize their lift-to-drag ratio, so that the air keeps them aloft as long as possible. Because of the short flight time and high risk of taking jump after jump, many elite ski jumpers use wind tunnel time to practice and hone their flight positioning, as seen in the video below.
Weather also plays a significant role in ski jumping; it’s one of the few sports where a headwind is an advantage to athletes. To try to adjust for wind effects, scoring for the sport uses a wind factor. (Image credit: T. Trapani; video credit: NBC News)

February 8, 2022
Beijing 2022: Why Are Ice and Snow Slippery?
Although every Olympic winter sport relies on the slippery nature of snow and ice, exactly why those substances are so slippery has been an enduring mystery. Michael Faraday hypothesized in the nineteenth century that ice may have a thin, liquid-like layer at its surface, something that modern studies have repeatedly found.
One recent study used an entirely new instrument to probe the characteristics of this lubrication layer and found that it is only a few hundred nanometers thick. But the fluid in this layer is nothing like the water we’re used to. Instead it has a viscosity more akin to oil and its response to deformation is shear-thinning and viscoelastic, more like the complex fluids in our kitchens and bodies than pure, simple water. They found that using a hydrophobic probe modified the interfacial viscosity even further, which finally provides a hint at the mechanism behind waxing skis and skates.
Fortunately for us, we’ve found plenty of ways to employ and enjoy water’s slipperiness, even as the mystery of it slowly gives way to understanding. (Image credit: M. Fournier; research credit: L. Canale et al.; via Physics World; submitted by Kam-Yung Soh)
February 7, 2022
PyeongChang 2018: Moguls
Moguls are bump-like snow mounds featured in freestyle skiing competitions and also frequently found on recreational ski courses. Although competition runs are man-made, most mogul fields form naturally on their own. As skiiers and snowboarders carve S-shaped paths down the slope, their skis and snowboards remove snow during sharp turns and deposit it further downhill. Over a surprisingly short amount of time, these random, uncoordinated actions form bumps large enough that they force skiers and snowboarders to begin turning on the downhill side of the bump. That action continues to carve out snow on the uphill side and deposit it downhill, effectively causing the downhill bumps to migrate uphill, as seen in the timelapse animation below. As more moguls form, their motion organizes them into a checkerboard-pattern that moves in lockstep. Observations show that mogul fields can move about 10 meters uphill over the course of a season. Seemingly, the only way to prevent mogul formation on steep slopes is to regularly groom them back to a flat state! (Image credits: J. Gruber/USA Today; J. Huet; D. Bahr; research credit: D. Bahr et al.)
February 13, 2018
PyeongChang 2018: Ice’s Watery Sublayer
The Olympic Charter declares that winter sports must be practiced on snow or ice. Both are frozen forms of water, which despite its ubiquity, is one of the strangest substances around. In addition to its tendency to expand as it freezes, ice is inherently slippery, and no one’s quite certain yet why.
Most people have heard the theory that ice skating is possible due to high pressure melting the ice beneath the narrow blade. But realistically, pressure melting should only work for ice down to about -3.5 degrees Celsius. By contrast, the ideal temperatures for figure skating and ice hockey are -5.5 and -9 degrees Celsius, respectively. Melting due to friction might account for slipperiness a few more degrees below freezing, but it doesn’t explain why ice can be slippery when you’re just standing on it.
When physicist Michael Faraday suggested in 1850 that ice has a thin liquid-like layer at its surface, many discounted the theory. But modern experimental techniques and computer simulations have shown that Faraday was right. Ice has a liquid-like layer some 1 to 100 nanometers thick at its surface, and this layer persists to temperatures below -30 degrees Celsius. The process is known as surface pre-melting and what causes it is an area of active research for physical chemists. Current theories include hydrogen bonding and even quantum mechanical effects. (Image credit: AP Photo/B. Armangue; research credit: R. Rosenberg; Y. Li and G. Somorjai; F. Paesani and G. Voth)
This opens FYFD’s two-week series on the physics and fluid dynamics of the Winter Olympics. Stay tuned! – Nicole
February 12, 2018