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LESTER HOLT, anchor: In the sport of Freestyle Aerials,
skiers are judged on their ability to perform complex jumps in the air.
Emily Cook, a 12-year veteran of the U.S.
Freestyle team, and The Exploratorium's Paul Doherty,
a physicist funded by the National Science Foundation,
show how these jumps actually come from three basic twisting techniques
that you can try yourself.
HOLT: It's a sport of seemingly endless twists and turns.
In Olympic Freestyle Aerials, skiers plummet down a steep ramp at up to
45 miles an hour before launching almost 50 feet into the air.
Then the real fun begins.
Olympic Aerialist Emily Cook is part acrobat,
part daredevil--and an intuitive master of physics.
EMILY COOK (U.S. Ski Team - Freestyle): I think I was kind of born to be upside down.
Some people are like that. It's my most comfortable position.
HOLT: Any rotating mass has a property known in physics as angular momentum ...
created when torque--a force causing a free body to rotate--
is applied to a mass, in this case an aerialist.
Aerial skiers call this "contact twisting," and they create it
in the way they push off the ramp.
COOK: If you were standing on the ground and you were to just jump up
and do a full twist, your pushing off of the ground is what is causing the twist.
HOLT: Paul Doherty, Senior Scientist at The Exploratorium in San
Francisco, shows how you can do "contact twisting" yourself.
Dr. PAUL DOHERTY (The Exploratorium): Watch me,
I'll leap into the air and turn 90 degrees by pushing on the ground before I leap.
That was easy!
HOLT: The push-off is crucial: once in the air,
aerialists cannot change their angular momentum.
So how do they control their motion to execute the best spin in the air?
By controlling what's called their "moment of inertia"--which they do
by moving their arms and legs in and out.
A good illustration of this comes from the animal kingdom.
Cat: Meow!
HOLT: For more than a century, scientists have studied why a
falling cat almost always lands on its feet.
Slow-motion photography reveals that by tucking its front legs and
spreading its back ones--all while rotating the upper and lower torso
in opposite directions--the cat can twist without touching anything.
Dr. DOHERTY: One part of the cat is turning one way and
the other part's turning the other.
By changing the position of the mass, they can actually turn in the air.
HOLT: Aerialists perform the "cat twist" by making a hula-hoop motion with their hips.
COOK: If you picture yourself in a pool and you bend yourself at your
waist, and you just kind of swivel yourself around, eventually you'll start twisting.
HOLT: The last technique, called "tilt-twisting," uses precise arm movements
to alter the speed and orientation of the spin.
COOK: If I were to go off the jump, I have both of my arms up,
and if I were to drop my left arm, if you think about every action has
an equal and opposite reaction, my body is going to go the other way.
Dr. DOHERTY: If I start out with my arms like this,
I'm going to rotate my arms, right one back and left one forward.
Watch that happens to my legs, and that was very effective in turning me.
HOLT: On the ground, twisting may look easy.
But six stories above the ground--with the whole world watching--
Olympic Freestyle Aerials is nothing less than a leap of faith in the laws of physics.