Aug. 18, 2000 -- To the observer, pole vaulting may seem fairly simple.
The athlete runs with a pole in hand, plants it in the ground and leaps over another pole.
But to a physicist, much more is at play. Consider this perspective:
As Sydney Olympics gold medal contender Stacy Dragila prepares to jump, she has chemical potential energy stored from the food she has eaten. She then runs down the path, converting her chemical potential energy into speed — or kinetic energy. Once she plants the pole, it begins to bend, slowing down Dragila’s kinetic energy and transferring it to elastic potential energy in the pole.
As the pole lifts her upward, it returns the potential energy to Dragila in the form of gravitational potential energy. By the time she clears the bar, Dragila has just enough kinetic energy remaining to carry her past the bar. On her way down, the gravitational potential energy becomes kinetic again and is finally absorbed by the mat she hopefully lands on.
Even Dragila tends to shrug off all the science of her sport.
The 29-year-old American who currently holds the record for women’s pole vaulting at 15 feet, 2 1/4 inches“ confesses, “Numbers don’t do anything for me. I’m thinking more about form.”
Predictions of Physics
But the numbers do matter to Dave Neilson, Dragila’s coach. He figures if science is what makes pole-vaulting work, then science can also help Dragila vault higher. And according to recent calculations by a couple of scientists, Dragila can vault higher — more than two feet higher — according to one physicist.
“Pole vaulting is almost strictly a matter of energy,” says Peter Watson, the dean of science at Carleton University in Ottawa, Canada. “So the limit is designated by how fast you can run carrying a pole.”
Calculations also show that men are reaching their height limit while women, who are relatively new to the sport, have a way to go.
Speed accounts for at least two-thirds of the height an experienced pole-vaulter clears. So calculating that pole vaulters, who must run with the pole in their hands, run slightly slower than the world’s fastest sprinters, Watson figures men should be able to clear 19.8 feet. That height happens to be short of the current world record, 20 feet, 1 3/4 inches, held by the Ukraine’s Sergey Bubka. But Watson figures even Bubka won’t be able to improve his record by much.
“Unless they run a lot faster, men cannot increase the height very much from there,” says Watson.
Meanwhile, Cliff Frohlich, a physicist at the Institute of Geophysics within the University of Texas, has taken Dragila’s sprinting times and calculated how high she should be able to vault, based on the men’s records. His estimate? Just higher than 17 1/2 feet.
Dragila is shooting for something a little less ambitious.
“I’m looking to break 16 feet,” she says. “I’ve come close in a couple competitions. I just have to put it all together in one jump.”
Not an Exact Science
As Dragila’s coach, Neilson, points out, converting the kinetic energy of the sprint into potential gravitational energy in the vault is difficult to execute without losing at least a little bit of energy in the process.
“There are a lot of very fast people who can’t vault very high,” says Peter McGinnis, a biomechanic at State University of New York in Cortland who advises the U.S. Pole Vaulting team.
McGinnis explains a lot of energy can be lost in the moment when a vaulter plants the pole and bolts into the air. If they take off too early, vaulters can lose the forward energy they need to get over the bar. If they take off too late, they lose energy in the sudden jolt of the bar on their shoulders. And if they plant the pole while their weight is on the heel of their foot, they lose energy through the arresting position of their heels.
“You want to be jumping off the ball of your foot as the bar hits the box,” says McGinnis, who also pole vaults and has cleared 15 feet. “And you want your limbs to be rigid.”
The Pole Factor
The pole, itself, also makes a big difference in how high a vaulter can leap. When the sport began at the start of the 20th century, athletes mostly used bamboo poles that were so limiting the early pole vaulters took their modest falls on a normal grass surface. After World War II, vaulters starting using metal poles, which were lighter. Eventually fiberglass poles entered the scene and their elasticity helped vaulting records soar. Today athletes use poles made from a composite of carbon fiber that offer even more bend and spring.
To take full advantage of the pole, says McGinnis, it’s better to grip it high up. That way the athletes’ center of gravity starts higher and they’re able to vault higher. For the same reason, being tall is another advantage for pole vaulters since their weight is centered at a higher level at the start of their jump.
Women are generally shorter than men (Dragila is surprisingly short for a pole vaulter at 5 feet 7 inches), which Frohlich figures hinders women’s vault heights by an average of nearly 2 1/2 feet. McGinnis also points out that women tend to have less strength in the upper body. Not only can that limit how high they push themselves off the top of the pole, it also means their average body weight is centered slightly lower.
Of course, pole vaulting isn’t all about science. Like any sport, it also requires mental focus. Jeff Hartwig, the American record-holder in the pole vault, learned that the hard way when he failed all three attempts at clearing any height at the U.S. Olympic trials last month.
As Dragila’s coach, Neilson says, “Even if we understand what needs to be done, actually making it happen is a whole separate thing. That’s what sport is all about.”