Downhill Science: Alpine Skiing
A downhill ski race is a tour de force--emphasis on force: from the forceful push-off that accelerates the alpine skier down the slope, to the forces of gravity, friction and wind or air resistance. NSF-funded scientists Paul Doherty of The Exploratorium in San Francisco, and Sam Colbeck, formerly of the U.S. Army Cold Regions Lab, explain the physics of alpine skiing, with help from four members of the U.S. Ski Team: Ted Ligety, Marco Sullivan, Scott Macartney and Julia Mancuso.
LESTER HOLT, anchor: In February, Olympic skiers will race down Vancouver’s Whistler Mountain at speeds of up to 90 miles an hour. Watch as scientists and researchers funded by the National Science Foundation explain the physics of this downhill thrill ride.
TED LIGETY (U.S. Ski Team – Alpine): You're trying to go as fast as you can but at the same time you're like, "Whoa, I'm going fast!"
MARCO SULLIVAN (U.S. Ski Team – Alpine): You’re trying to get your body to go faster and faster.
HOLT: Downhill skiing is a nail-biting, edge-of-your-seat thrill for the viewer, and a seemingly death-defying feat for the athlete.
SCOTT MACARTNEY (U.S. Ski Team – Alpine): You have speeds that reach 90 miles an hour, and probably the fastest I’ve been clocked out is 97.
HOLT: Think of a downhill race as a “tour de force” – emphasis on force – right from the start.
JULIA MANCUSO (U.S. Ski Team – Alpine): I take a couple of deep breaths and clear my mind and then kick out and go.
HOLT: It’s Newton’s Second Law of Motion: a force – here it’s “kicking out” and pushing off the snow, on an object, in this case the skier, produces an acceleration, down the slope. Then, one of the fundamental forces of physics, gravity, takes over.
SULLIVAN: It’s like, just gravity, ripping you down this mountain.
Dr. PAUL DOHERTY (The Exploratorium): The entire bulk of the earth pulling these skiers down, accelerating them to high speeds.
HOLT: At the same time, another force is working to slow the skier: friction, created when the bottom of the ski rubs against the surface of the snow, even a surface groomed and “polished” to minimize friction.
Dr. SAM COLBECK (U.S. Army Cold Regions Lab): They'll prepare these snow surfaces but it may snow or it may melt or there may be windblown snow deposits.
HOLT: How the skier “holds” his skis on the surface of the snow can greatly impact the skier’s speed.
DOHERTY: The forces of the snow on the skier can be reduced by perfectly edging as they come down, or floating across the snow.
HOLT: “Edging” the skis causes one side to dig in, slowing the skier down, giving him more control on alternating left and right turns. Keeping more of the ski flat on the snow causes the ski to sink less, and maintain higher speed.
MACARTNEY: You have the gravity, you have the resistance of the snow, but the real big factor is the wind resistance.
HOLT: Wind, or air resistance, is another force that can slow the descent. Skiers try to minimize it by keeping their body small, and tucked in.
MACARTNEY: So we spend time getting our profile as low as possible and as long as possible so that we eliminate as much wind resistance as we can.
HOLT: Finding the shortest path-length down the hill also involves staying close to the surface of the slope when going over jumps and bumps.
LIGETY: You end up hopping the jump you go so much higher and then you're in the air longer, slowing yourself down.
HOLT: Closely following the curve of the slope can also help skiers find the shortest route, what they call the “line”, down the mountain.
DOHERTY: The skier has to look at the bumps and hollows in a ski slope and pick a path down. Finding that line is the art of going fast.
HOLT: And crossing the finish line.
Announcer: Marco Sullivan for the United States!
SULLIVAN: It’s one of the greatest feelings, when you actually make it to the bottom, and you survived it, and you’re, like, “alright, that was awesome. You know, let’s go do it again.”
Announcer: That is excellent!
HOLT: The force of gravity, the fight against the forces of snow and wind, makes downhill skiing one of the most thrilling events in the Winter Olympics.