Figure Skating Dynamics of Leaps and Throws

In figure skating, a leap is a move where a skater leaves the ice to jump into the air. Some of the many types of leaps include the waltz (a half-turn rotation), loop (where a skater takes off and lands on the same foot), and Salchow (similar to the waltz jump; it was originated by Swedish World figure skating champion Ulrich Salchow).

A throw, in pairs figure skating, is a move in which usually the man propels the woman into the air; however, in similar pairs competitions a pair of women or men compete. The throw was invented by American Olympic figure skater and World and Olympic figure skating coach Ron Ludington. The first type of throw was the throw Axel, named after its Norwegian inventor Axel Paulsen. Since then, many different types of throws have been invented, including the throw loop, throw Salchow, and several types of death spiral throws. Throws are also classified as to the number of rotations: single, double, triple, and quadruple.

Throws involve physics because as a skater leaves the ice to jump into the air, several simultaneous forces are in play. A force, in physics, is defined as a physical action that tends to alter the position of an object with mass, and is equal to the object's rate of change in momentum. Simply said, it is the push or pull one object exerts on another object so that an action can take place. In figure skating, for instance, a skater pushes off the ice in order to be propelled upward into the air. Whether it is a leap or throw in figure skating, the basic dynamics are similar. In the case of the leap, only the skater preparing to jump is involved in propelling oneself into the air. While in the throw, one partner helps to propel the other skater into the air.

One force involved in a leap is the horizontal force of the skater's blade across the ice. Its force is directly related to the speed of the skater going into the leap. If the skater is moving slowly—that is, possessing a small amount of linear momentum (straight-line motion)—the force will be smaller than if the leap is begun with a greater speed, with a larger amount of linear momentum.

Horizontal momentum can also be converted into vertical momentum. This vertical force is exerted by the combined efforts of the skating ankle and knee, the free leg, and the arms. As a skater increases in speed, the skate toe is hurled into the ice and the leg is used to propel the skater upward. The faster a

Zhang Hao (L) of China throws his partner, Zhang Dan, during their short program of pair event in the figure skating Grand Prix series final in Tokyo, 2005.
skater's speed when preparing for a leap, the higher and farther the skater will be able to jump. These actions—the kick of the leg, along with the push of the ankle and knee and the upward movement of the arms—provide vertical thrust for the leap.

Another force involved in a leap is the rotation of the skater. This rotation involves horizontal and vertical forces being applied to rotate the skater. The rotational force is provided initially by the lifting action of the outside arm. Thus, angular momentum is carried into the leap by applying a torque just like a spinning top. When the skater is in the air, the arms are positioned close to the body to make the rotation faster. The skater also stretches out the body, along with positioning both legs close to one another, to order to speed up the rotation.

The dynamics of jumps are rapidly gaining importance as competitive figure skaters add new and more difficult moves to their repertoires. In the 1980s, triple jumps were considered the most difficult jump. In the 2000s, quadruple jumps—in which a skater must jump high enough and spin fast enough to rotate four times before landing—have become more common in international competitions. Triple Axels, triple Lutzes, and triple Salchows are also complex jumps that are becoming more common in competitions.

To look at the mechanics of the jump, experts in human biomechanics (the scientific study of motions) use high-speed cameras and computer analysis programs to measure the speed and height of jumping skaters. Reflective markers are placed at various locations on the skater's body so that video cameras can record the ever-changing positions. The computer software analyzes the recording to determine such data as the most effective jump height, body position, and rotational energy. Three-dimensional images show the various jump stages so that modifications and improvements can be made to the skater's performance.

Research has shown that the height and length of a jump are proportional to the horizontal and vertical forces generated at takeoff. If the vertical thrust (energy generated by arms, knee, ankle, and leg) is much greater than the horizontal force (speed on ice), then the jump will be high in altitude, but not very long in distance. If, however, the horizontal force is greater than the vertical thrust, then the jump will be long, but not very high. Proper planning and integration of these jump forces are important to ensure that the jump is performed properly.