On Tuesday, Americans woke up to the news that Emily Sweeney of Team USA crashed during her luge run at the Olympics. Sweeney refused a stretcher and was able to walk away from the frightening accident — a tough-as-nails moment after careening down what’s essentially a roller coaster made of ice. Sweeney crashed after losing control during her final heat at Curve 9 — already notorious among Olympic sliders before the games even began.

The insane physics of the Winter Olympic’s “fastest sport on ice” means that coming out of a curve during the luge feels like, in the words of 2014 Olympian Chris Mazder, “launching into space on a rocket.” Sliders can reach speeds of 90 miles per hour after launching onto the ice with a 50-pound sled, propelling forward with spike-equipped gloves, and steering with their calves.

All that speed means that luge races are timed to one-thousandth of a second, and any time lost on a curve can ruin an athlete’s chances of placement. Defending Gold medalist Felix Loch of Team Germany bumped into Curve 9 on Sunday, losing hundredths of a second and his chance at a 2018 medal.

Luge races take place on a track built with a length of 1,000 to 1,500 meters with a difference in elevation between 110 to 130 meters and an average slope of nine to 11 percent. Curve 9 is just one of 16 obstacles on Pyeongchang’s Alpensia Sliding Center track. As the athletes shoot down the U-shaped groove of the course they have to maneuver through left curves, right curves, hairpin curves, S-shaped curves, and a three-turn combination called a labyrinth.

But it was Curve 9 that everyone had been talking about before the Olympics kicked off. Before her own run, Sweeney described the curve as like “driving on a slanted road, but having your call getting pulled in a direction away from the way you’re steering.” It’s the angle of the curve that’s so rough — the turn sends the lugers to the right, but the track is actually designed to go 45 degrees to the left.

And when lugers hit the angle of the curve, their force against the ice can be as high as eight times that of gravity. The aerodynamic position of their body combined with the tiny amount of contact the steel (the name for the sled’s blades) makes with the ice minimizes the force of the drag, adding incredible speed to the centrifugal force that emerges as a reaction between the ice, the athlete, and the inertia. All of that means when a curve shoots you to the right, but the track goes to the left, retaining control is going to be incredibly difficult.

It’s ultimately what got Sweeney, who began sliding at severe and alternating angles after losing control after Curve 9. She was ultimately thrown from her sled into a tumble — a scary finale for a first-time Olympic run.

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