The Physics of Pole Vaulting
Olympic gold medalist Stacy Dragila
In September, American Stacy Dragila became the first woman to win an Olympic gold medal in women's pole vaulting at the Olympic 2000 games in Sydney, Australia, clearing a height of 15 feet 1 inch. And a physicist from the University of Texas says women are poised to make even bigger leaps in the record books. Cliff Frohlich, who has written articles on sports physics in the American Journal of Physics and the book The Physics of Sports, points out that while the men's pole vaulting record has stood for more than 6 years, we've yet to see the heights to which women will vault.
By using a vaulter's sprint speed to determine the potential vertical height, Frohlich says he expects the women's record to top 17.5 feet soon. That's more than two feet higher than where the current record sits. (You can determine your own potential vault height online, and read more about the physics of pole vaulting — including the equations Frohlich uses to determine vaulting heights — at www.aip.org/physnews/graphics/html/polevault.html.) For example, at 5 feet 8 inches, with an approximate sprint speed of 18.7 MPH, Dragila, an assistant track and field coach at Idaho State University and the women's current world record holder, should theoretically be able to jump a height of about 14 feet 9 inches.
Dragila has already topped that approximation, setting her current record of 15 feet 2.25 inches in July at the Olympic trials in Sacramento, California. (The world record in men's pole vaulting is held by the Ukraine's Sergey Bubka, who cleared 6.14 meters or 20 feet 1.75 inches in a 1994 competition.) She fell short of her attempts to clear 15 feet 3 inches during the actual Olympic competition, but says she has cleared that height during practice sessions. Still, notes Frohlich, "the model predicts the height attained remarkably well." The difference is accounted for by the fact that the sprint speed used is only an approximation, and no other factors are considered.
Dragila's coach, Dave Nielsen, agrees with Frohlich that women probably have room for significant gains, but he isn't sure about the 17.5 foot figure. Still, he thinks 16.5 feet is a good bet, and he says women will eventually break the 17 foot mark. "Women have different challenges than men in pole-vaulting, such as different upper body strength and a lower average height," Nielsen says. Nevertheless, he adds, "I don't doubt that women will eventually jump over 17 feet," as women pole vaulters continue to increase sprint speeds and improve other vaulting factors.
With current women's records at just over 15 feet, Frohlich says that "the women's record is likely to improve quite a bit" as women who can run faster and use the pole more effectively enter the field. The reason this is possible is that vaulting is an example of conservation of energy: The kinetic energy, of the runner's approach speed is converted, through the pole vault, into the potential energy of the jump height. The faster a vaulter sprints toward the vault bar, the more energy is available for the vault.
Nielsen says in addition to the approach velocity, other factors must be considered, such as how effectively the vaulter's horizontal running velocity is converted into vertical velocity, since this determines the amount of momentum that will carry the vaulter up and over the bar. This occurs through the "angle in" and "angle out" that the vaulter's body makes with the ground at the start of the vault.
Upper body strength and the height of the vaulter's center of mass also play very important roles, since both are intimately tied up with the amount of mechanical work that must be done. The taller a person, the higher is their center of mass. Likewise, the distribution of mass affects center of mass. In general, men have a higher center of mass than women do.
In his recent presentation before the 2000 Olympic Trials USA Track & Field Super Clinic, Nielsen stated that everything else being equal, "the taller vaulter will likely be able to hold (the pole) higher and will be higher in the air at take off." As for upper body strength, Nielsen says, "Females are similar to males in leg strength, but have noticeably less upper body strength." He thinks this might be a liability during vaulting, which requires the execution of a series of maneuvers that amount to a somersault while holding the pole.
Louis Bloomfield, another physicist who teaches the popular "How Things Work" course at the University of Virginia agrees with Frohlich's expectations that women will likely make some big height gains in the near future. "He's probably correct," says Bloomfield. "His observations that women can do better than 15 feet, and will probably do so fairly soon, is probably correct, too."
-Inside Science news team
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