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Sat February 22, 2014
Getting Technical: Questions And Answers About The Winter Olympics
Originally published on Sat February 22, 2014 9:41 pm
Events in the Winter Olympics can be highly technical, with arcane rules and specialized equipment that can defy easy explanation. On the question-and-answer site Quora, several interesting topics have come up in recent days, from why athletes use tape on their sleds to how a human can surpass 80 mph on skis.
We've been sifting through the questions people ask about the Sochi Games on Quora. As you might expect, one of the longest and most detailed exchanges (too long and detailed to fit in this post, in fact) centers on the controversial win by Russia's Adelina Sotnikova in women's figure skating.
Here are some of our favorite questions, with answers:
Answered by Jim Bell, Executive Producer, NBC Olympics:
Answered by Liz Lewis, Curling since 2006 at the Mayfield Curling Club, Cleveland, OH, USA:
To expand on what was already said, curling ice isn't smooth like skating ice. It's covered in little bumps, which is referred to as the pebble of the ice. So, sweeping melts the pebble down a bit to maintain speed or the trajectory of the rock.
The pebble is what makes the rocks curl. Without that pebble, you really can't control the path of the rock. I hope that helps!
Answered by Brad Stewart, Athlete US Skeleton Team, Sundance Developer, Real Estate, Web Duder:
A skeleton sled has a soft-ish (think yoga mat) covering over the sled that makes it a flat surface and covers all the internal components. A special type of gaffer type is used to hold the covering to the sled.
The best tape is made by a company in Europe called Tesa. Each roll is around $60 and we hoard it since it's difficult to come by. The reasons we seek this brand out are because:
- It maintains its hold and flexibility when wet and cold.
- We often need to get into the sleds daily for modifications and inspections and it doesn't leave any sort of residue like your typical duct tape leaves.
- It had more grip than duct tape so you maintain contact with your sled.
"I was just watching Bode Miller's final training run, and at the bottom of the course, he got up to over 81 mph. Whoosh! How is that possible if terminal velocity - falling at a 90 degree angle to the earth with only wind resistance - is 120 mph?"
Answered by Mark Eichenlaub, PhD student in Physics:
The numbers you cited actually work out exactly like you'd naively expect.
The force of wind drag is proportional to velocity squared. 120 mph (falling) is 1.5 times as fast at 80 mph (skiing). That gives a force 1.5^2 =2.25 times as great. In other words, when you're skiing downhill at 80mph, you experience a bit less than half as much wind resistance as at 120 mph.
At a 30-degree slope, the force pushing you down the hill is exactly half your weight. So compared to a sky-diver, our skier has about half as much force pushing him down the hill and a bit less than half as much wind drag. So this speed is entirely reasonable.
To try to get more accuracy, you'd have a lot of things to consider:
- The friction between the skis and snow. This friction force is not very large; the course is designed to be very slick and fast; they're essentially skiing down ice. However, friction varies throughout the run as the skiers turn, accelerate, etc. Friction is, after all, how the skiers control themselves. Additionally, as Kari pointed out, the skiers may actually push off at some points of the run to get the frictional force to point down the hill, not up it.
- The position of the skier. 120mph is not a hard-and-fast limit to how fast a person can fall through the atmosphere. Terminal velocity will depend on the aerodynamics of your position. Skiers crouch down, and this affects the wind drag on them. Additionally, aerodynamics around the ground are not identical to aerodynamics through free atmosphere.
- The altitude. The course is at about 2000m of elevation. Air is about 20% thinner there than at sea level.
- Slope. The course seems to have an average slope of 18 degrees, according to Rosa Khutor Alpine Resort, but is as steep as 40 degrees near the top. Skiers don't follow an exact gradient down the hill, so the path they take also matters.
Especially because we don't know the frictional forces, it's hard to get a highly-accurate estimate of how fast skiers should be expected to go. Indeed, by controlling the friction, gradient, and air drag, skiers can traverse the same course at a wide range of speeds. However, 80 mph is not at all unreasonable.
Answered by Andy Warwick, Wrote and edited some Sochi 2014 educational materials:
Ski jumpers are judged on two elements: distance and style. Let's start with the latter, since this is the crux of the question.
Style: There are a maximum of 60 points awarded for style and competitors are judged on the technique not only of the flight itself, but also the timing of their take-off, the landing and movement down the hill after landing, called the outrun. During the jump judges are looking for aerodynamic efficiency, ski position (the 'V'), the position of the arms and legs and fluidity of movement between take-off, flight and landing positions. Jumpers thus receive style points in three areas: flight, landing and outrun.
The perfect flight:
- begins with a "bold and aggressive take-off"
- includes rapid, smooth transitions between flight positions
- is symmetrical
- is stable
- is with legs fully stretched
Judges can deduct 5 points at their discretion.
The perfect landing sees the jumper:
- raise their head
- lift their arms forward, up and to the side
- move from the 'V' position to one with parallel skis
- split their legs
- bend their knees
- place one foot slight ahead of the other (called the 'telemark' position)
Judges can deduct 5 points for landing; 2 points must be deducted for failure to adopt a true 'telemark' position.
The perfect outrun sees the jumper:
- hold the 'telemark' position for 10-15m
- pass the 'fall line' in a stable and relaxed posture
Judges can deduct 7 points for the outrun; jumpers receive the maximum deduction for falling before the 'fall line'. Points are deducted generally for losing balance or touching the snow with anything but the skis.
There are five judges. The three middle scores are added together while the highest and lowest are discarded.