One by one the world’s best snowboard jumpers will hurl themselves down a steep ramp, fly off a giant cliff of a jump and—while hurtling through the air—execute sequences of flips and twists so fast and intricate that you’ll need slow-motion replay to even see them happen.
Big air snowboarding makes its Winter Olympics debut this month in Pyeongchang, South Korea, along with mass start speed skating and curling mixed doubles. The snowboarding event is likely to be a big draw, with its 49-meter-high ramp—one of the world’s tallest—creating the potential for breathtaking new tricks as well as some spectacular and potentially dangerous wipeouts.
To excel in this competition, snowboarders will have to control their nerves and adrenaline while intuitively mastering the physics of angular momentum, energy conservation and snow thermodynamics, along with projectile motion (with themselves as the projectiles). Then there is the landing: A mistimed pop off the jump or one trick too many could lead to a broken wrist, ankle, knee or worse on the quick return to Earth.
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“Some of the performers probably will develop new tricks, because this is higher than previous competitive jumps,” says Michael O’Shea, a physicist at Kansas State University who has written and taught about the physics of outdoor sports. But with the new opportunities come new challenges. Because the athletes will spend more time in the air, O’Shea points out, they will have to make more adjustments for wind velocity. And if the light or visibility is bad, “hopefully they have a timer in their brain about how long they can twist in the air,” he says. “It’s hard to see that surface coming at you when you’re traveling at 50 miles per hour.”
Snowboarders to watch this year include Max Parrot of Canada and Austria’s Anna Gasser, who both won first place late last month at the Winter X Games in Aspen, Colo. Parrot led the men’s pack with an impressive cab 1800 triple cork and a front triple 1440. That means making five complete rotations while sideways and oriented opposite one’s natural stance, and four complete spins oriented front side. (The numbers are the degrees of rotation.) At the X Games, Parrot stuck the landing each time.
In terms of physics, what sets Parrot, Gasser and other front-runners apart from their competition is their ability to almost instinctively manipulate their bodies in complex ways to rotate, twist and move in midair, while taking advantage of the angular momentum they get when they push off the ground—a factor they cannot change once they are in the air. Any object rotating around an axis, like a spinning top, tends to continue rotating at the same rate of speed unless something gets in its way, or if it changes its shape. (Angular momentum is a product of the moment of inertia—how “spread out” the spinning person is—and how fast they are spinning.) If snowboarders pull in their arms while in the air, for example, they rotate faster; sticking the arms out does the opposite. The total amount of angular momentum, however, stays nearly the same—except for a little lost to air resistance. So if the rotating boarder pulls limbs in, lowering their moment of inertia, the rotation speed has to go up to keep that momentum constant.
“If a cat falls from some height, it can twist itself and land on its feet. It’s the same way for snowboard jumpers—but it’s like falling down from a 16-story building,” says Maruša Bradač, an astrophysicist at the University of California, Davis, who teaches a course on the physics of “California sports,” which also include skiing and surfing. A falling cat will tuck in its forelegs to one side and stretch its rear legs out in the opposite direction, changing its moment of inertia so the front part of its body briefly rotates faster, thus making it possible to twist without pushing off of anything. Unlike a cat, however, the rider’s feet are strapped to a board.
Furthermore, the precise shape of the jump affects an athlete’s momentum; for example, a jump that curves sharply upward would induce backward rotation. A snowboarder could also get an extra unexpected angle at takeoff from changeable features in the snow, such as an icy groove worn by previous riders. This could directly affect tricks and landings—the point at which most injuries occur. “I believe you could design a jump that had safety built into it with regard to the impact,” says James McNeil, a physicist at the Colorado School of Mines who has modeled winter terrain park jumps. “It doesn’t mean you won’t get hurt, but the likelihood of injury is reduced and the severity of it, should you be injured, is reduced.”
“These [snowboarders] know what they’re doing; they’re able to control their bodies in flight. For them the issue is how hard they come down,” says Mont Hubbard, McNeil’s colleague and a mechanical and aeronautical engineer at U.C. Davis.
Most snowboard jumps have a takeoff point followed by a flat area over which the riders perform tricks, and then a landing area that slopes downward at a maximum of 40 degrees. Many snowboarding injuries occur when riders fall onto the flat area; but PyeongChang’s jump does away with it, and has only the downward slope for them to land. Physicists quantify potential impact in such situations using the concept of “equivalent fall height.” A person falling straight down from 49 meters would certainly be injured. But when a snowboarder lands at an angle and keeps moving down a slope, the impact is equivalent to falling from a much lower height; some of the boarder’s gravitational energy gets translated into forward-moving energy. Therefore, landing on a steeper downward angle is safer. For one thing, the knees have far less energy to absorb.
“During the [jump] design phase we look carefully at all measurements and flight curves while considering takeoff angles and landing angles,” Roberto Moresi, contest director for park and pipe of the International Ski Federation (FIS), wrote in an e-mail response. “A good jump is when landing, they barely feel the impact, and that is our goal.” The International Olympic Committee recognizes the FIS as administering skiing and snowboarding competitions at the world level. To design and maintain the jump, the PyeongChang Organizing Committee for the Olympics and the Korea Ski Association contracted Schneestern, a sports infrastructure company based in Germany.
Despite all the physics precautions, Moresi expressed some concern about the weather—a variable the organizers cannot control. The athletes will have a tough time if the event is beset with heavy snow, strong winds or thick fog, or if ice and ruts build up along the track. But if weather conditions cooperate, nothing will be more important than what a rider does in those thrilling few seconds between launch and landing.