to Videolink arrow

Newton logo to print

Ski Jumping

 

Overview

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 akeoff 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.

Activity

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. Materials
  • 1 meter (3.3') of Styrofoam pipe insulation, cut lengthwise
  • marble or small steel ball
  • 8 to 10 thick books or bricks or a chair
  • masking tape
  • tape measure
  • table
  • paper and pencil
1. Start building your "inrun" by piling several books on a table so that they measure about 30 cm (12") high. Place one end of the pipe insulation right on the edge of the table, and put the other end under one of the books at the top of the stack. Build up several books under the middle of the ramp so that it doesn't sag or bend. Secure the insulation to the table and books with masking tape, making sure you don't tape across the track. 2. Place your marble at the top of the ramp. Without pushing, let it roll. Observe the flight path and the place where it first lands on the floor. Repeat this step four more times so that you can get a consistent reading. Remember to start from the same place each time. Measure and record this distance under the heading "flat track" and draw the shape of the marble's flight path. 3. Remove the books holding the middle of the ramp and adjust it so that it curves down to the table and runs flat along the table for about 20 cm (8") before it reaches the end. Make sure that the end of the ramp still lines up exactly with the edge of the table and once again secure it with masking tape. 4. Using the same marble as before, test the ramp again. Remember to start from the same place. Record the distance under the heading "curved track" and again draw the flight path of the marble. 5. Repeat step 4 but this time add a book to the end of the ramp so that instead of lying flat on the table, the ramp curves down and back up a bit. Record your measurements under the heading "U-shaped/one book" and draw this flight path. Questions

Resources

    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:
    http://www.oslo.sintef.no/gemini/1993-dec/11.html
    Jump: The homepage dedicated to ski jumping:
    http://www.cdnsport.ca/jump/