Brian hits the slopes to learn how ski jumpers go so high and
Segment Length: 7:30
How do the shapes of objects affect the flow of a fluid? Mix one quart of white Ivory dishwashing liquid with five drops of food coloring and place in a shallow baking pan. Try dragging different-shaped objects through the liquid and observe the flow patterns they create. The more swirls, the more turbulence and the less aerodynamic the shape. Based on this experiment, why do you think manufacturers don't make skis with square fronts?
Have you ever skied over a large bump and become airborne? Why do you think that happens? Do you watch the ski jumpers during the Winter Olympics? How far do the jumpers go before landing? Why do they hold their skis and their bodies a certain way?
There are few feats as breathtaking as a perfect ski jump. Hurtling down a snow-covered ramp at speeds in excess of 100 kilometers (60 miles) per hour, the skier literally dives off a cliff, soars through the air, and finally descends back to earth some 100 meters (328 feet) from takeoff.
To a novice, the steps in a ski jump look deceptively simple. In reality, each involves a complex balance of forces where only slight changes in equipment or body position can mean the difference between a gold medal and disaster.
Like a roller coaster, all the energy for a jump comes from gravitational potential energy acquired by going to the top of a hill - in this case, the inrun. Coming down the inrun, jumpers try to build up as much speed as possible while maintaining control. To minimize air resistance, they get in a low crouch, point their arms forward, and bend their heads slightly downward like a diver entering the water.
Halfway down the inrun, jumpers begin to re-position their bodies in preparation for leaping off. Near the end, where the inrun begins to curve upward, they raise their hips slightly while pressing the chest tight against the knees. This makes their legs act like a coiled spring storing additional energy for the takeoff. About three meters (10 feet) from the end of the inrun, jumpers begin their final adjustments before takeoff, bringing their arms perpendicular to the ground and rising up slightly.
The most important part of the jump occurs at takeoff. Within a tenth of a second, jumpers must combine two motions at once, leaping both forward and upward at the same time. The timing of the takeoff leap is what makes or breaks a jump. If jumpers spring before they reach the exact end of the takeoff table, their skis will point down, causing extra wind resistance which results in a short jump. If they spring too late, their skis are pointed too high, resulting in a serious loss of control.
In the air, jumpers become flying projectiles, using their bodies and skis like a giant airfoil. They lean forward, producing a positive angle of attack on the wind. Traditionally, jumpers always kept their skis straight in line with their bodies to lessen air resistance and reduce drag. In 1989, a jumper revolutionized jumping by holding his skis in a large V with the open end pointed forward. This positioning increases the surface area below the body, providing more lift toward the end of the flight. It extends the time in the air and the distance of the jump.
Botterill, S. (1994, Feb) V for victory. Life, p. 94.
Finkel, M. (1994, Jan) Leap of faith. Skiing, p. 26.
Friedman, J. (1994, Feb) This joint is jumping. Skiing, p. 22.
Roessing, W. (1995, Jan) Ramp champ. Boys' Life, p. 18.
Rosenberg, D. (1995, Jan 16) High-tech skiing. Newsweek, p. 63.
Ulmer, K. (1996, Feb) To air is human. Skiing, p. 70.
Wolff, A. (1994, Feb 7) Flight of the Finns. Sports Illustrated, p. 82.
Wolff, A. (1994, Feb 28) Jens Weissflog, ski jumper. Sports Illustrated, p. 55.
Giving jumpers a lift:
Jump: The homepage dedicated to ski jumping:
Vary the angle of a ramp and chart your flight path.
Ski jumping converts gravitational potential energy to kinetic energy. The objective is to launch a human projectile as far as possible. By manipulating a track, you can discover how changing the launch angle will change the direction and duration of flight.
The lift produced by ski jumpers is affected by the angle at which oncoming air hits their skis. Position a flat cardboard edge in front of the flow of air from a hair dryer. Tilt the cardboard progressively higher. Which angle produces the most lift? Can the angle of attack ever be too steep?
To decrease friction, skiers use waxes on their skis. Using two blocks of wood, test different substances on their surfaces to see which offers the least resistance when you slide the two blocks past each other. Try oil, wax, and ice.
Ski jumpers are always changing the position of their bodies during the jump to minimize air resistance. To see how this works for yourself, go for a bike ride and feel the wind blow. How do you have to ride to get the least resistance? What similarities and differences are there between bike riders and ski jumpers?
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