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LIAM McHUGH: It's a high-flying, gravity-defying
freestyle skiing event making its Olympic debut in Sochi,
Russia - ski slopestyle. One of the leading contenders for the
United States is 19-year-old Nick Goepper, one of the top
slopestyle skiers in the world.
NICK GOEPPER: Slopestyle is to me one of the most fun things
that you can do on skis and to be able to do that at a
competitive level in the Olympics and have that amount of
exposure and that amount of eyes on us at once I think is going
to be a huge opportunity.
McHUGH: Slopestyle skiing takes place on a downhill course with
a series of features such as rails and jumps that Goepper
must ski, grind, and jump off to impress the judges.
GOEPPER: You have the run mapped out in your head and you know
what moves you're gonna do and what grabs you're gonna get and
what rails you're gonna hit.
McHUGH: Goepper nails his tricks by relying on physical skill and
the laws of physics.
JORDAN GERTON: When you see an athlete that's just being
incredibly brave and just launching themselves out into
the air with no safety net, relying on their skill to land
them properly, then I think it's, you know, it's amazing
when they do it well.
McHUGH: Jordan Gerton is an associate professor of physics
at the University of Utah and supported by the National
Science Foundation. To understand the physics
of slopestyle skiing...
PRODUCER: Just act kind of natural like we're not here.
McHUGH: ...we filmed Goepper with a high-speed camera to capture
his every move on the slopes. Before pushing off at the top of
his run, Goepper is loaded with potential energy, or stored
energy. As he skis down the course, that energy is mostly
converted into kinetic energy, the energy of movement.
By bending his knees as he approaches a feature, Goepper
is loading himself with additional potential energy
to launch into the air, what he calls "popping off."
GOEPPER: Popping off of a jump or off of a rail basically means
jumping off the end of the takeoff of the rail or the jump
and that just initiates your height and your airtime.
GERTON: If you think of a spring and you take each end of the
spring and you compress it, then you've put potential energy
into the spring.
McHUGH: In order to perform his tricks, Goepper relies on a
property in physics known as angular momentum created when
torque, a twisting force, is applied to an object, or in this
case, his body. The more angular momentum he creates, the greater
the potential to spin.
GOEPPER: Your body is a key factor in how you initiate spins
and keep spins solid in the air.
GERTON: They're exerting torque on their skis through their
boots, through their ankles, their knees, and the rest of
their body and again that's sort of like loading up this spring,
except for now the spring is a twisting spring instead of
a compressing spring.
McHUGH: Once Goepper is airborne, he cannot change his
angular momentum, but he can control his rotation speed by
using his arms to increase and decrease his moment of inertia,
the resistance an object has to a twisting force.
GERTON: Start with your arms out. You ready?
STUDENT: Yep.
McHUGH: Gerton shows how moving one's arms closer and further
away from the axis of rotation changes the moment of inertia.
GERTON: So by changing whether how much of your mass, your arms
and your legs and your skis are close to your body, close to the
center of your body or farther away, you can control how fast
you spin and rotate.
McHUGH: This same concept is what makes Olympic aerialists
and figure skaters spin effortlessly. When Goepper jumps
or twists onto a rail, he relies on another physics concept to
control his motion - friction - the resistance created by one
surface or object moving over another.
GERTON: Their skis are exerting friction on the rail and vice
versa and that helps them to control their speed
while they're sliding.
GOEPPER: Rails are I think probably what I think is the
most fun aspect of what we do. You're sliding on metal and not
snow and it's really cool though because you can use your edges
of the skis to change your momentum.
McHUGH: By mastering the physics of slopestyle skiing, Goepper
hopes to have all the momentum he needs to land on the podium
at the 2014 Olympic Winter Games.
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