This week, people around the world have been watching the 2018 Winter Olympics. Pyeongchang, South Korea, is the site of this year’s games. Pyeongchang is a county located about 110 miles east of South Korea’s capital, Seoul. The area’s motto is “Happy 700,” which refers to the fact that Pyeongchang is 700 meters (2,297 feet) above sea level. Because of its snowy mountains, many people compare this region in Korea to the Alps in Europe.
Pyeongchang’s mountains provide the geography and climate necessary for outdoor winter sports like skiing and snowboarding. However, last Sunday, February 11, some of the most exciting action was indoors at the Gangneung Ice Arena. U.S. figure skater Mirai Nagasu made history. The 24-year-old athlete completed a difficult jump called a triple Axel. While a triple Axel is part of the routines of many male Olympic figure skaters, this is the first time an American woman has successfully landed the jump at the Olympics. Her score of 137.53 helped the U.S. team win a bronze medal in the figure skating championship.
Although Nagasu performed a triple Axel for the world this week, she has actually been training to make the jump for several years. It is also not the first time that Nagasu performed it while competing. At the U.S. International Classic in September, Nagasu became the third-ever American woman to land the jump in competition.
“When I started to land it, it was very satisfying,” Nagasu said last September. “I could always visualize myself doing the jump; it was just getting my muscles to react as fast as they needed to. Now, in practice, it’s a very consistent jump for me.”
The Most Difficult Jump
When performing a triple Axel, a skater must hurl his or her body into the air. The skater must then rotate three and a half times before landing back on the ice. An Axel is considered to be the most difficult of skating jumps.
The jump receives its name from its creator, Axel Paulsen, who developed it in 1882. The Norwegian skater performed what would today be called a single Axel. Paulson took off from the forward outside edge of one skate. He then spun one-and-a-half times in the air before then landing on the back outside edge of his other foot. Today, when a skater performs a double Axel, he or she spins two-and-a-half times. A triple Axel requires three-and-a-half spins. There have been no reports of any skater attempting a quadruple Axel.
Even though they are so difficult to perform, skaters want to perform double and triple Axels because each of these jumps can earn them extra points in competition. The base value of a double Axel is 3.3 points, while a triple Axel is worth 8.5 points.
The Science of Spinning
In order for a skater to perform a triple Axel, he or she must take into account the science of how and why things rotate.
In 1686, English scientist Isaac Newton published his famous three laws of motion. Newton’s three laws help explain why objects in the world move the way they do. Newton’s first law of motion states that any object will either remain at rest, or move in a straight line, unless it is acted on by another external force. According to this law, a figure skater will either stand still on the ice or travel in a straight line unless acted on by an external force. Since a skater performing a triple Axel is neither at rest nor moving in a straight line, there must be an external force that allows that skater to spin.
The force that allows figure skaters or any object to move in a circle is called centripetal force. Centripetal comes from the Latin words centrum, meaning center, and petere, a verb meaning to seek. A centripetal force is a center-seeking force.
For example, if you spin a ball attached to a rope around your head, the ball moves in a circle. This happens because the rope transmits a centripetal force created in the muscles in your hand and arm. If the rope happens to break, the ball is no longer controlled by the centripetal force from your muscles conducted through the rope. Without the centripetal force, the ball just flies off in a straight line.
Where does the energy needed to complete a triple Axel come from? Some of that energy comes from the speed at which a skater launches into a jump. However, that speed alone is not strong enough to complete a triple Axel. A skater must also rely on centripetal force.
Once skaters are in the air, they must pull in their arms and legs tightly. Next, they cross their ankles and hold their elbows. This tight body formation helps minimize air resistance. Also, the tighter a skater’s body is, the more centripetal force he or she is able to generate. It is likely impossible to complete a triple Axel without understanding how centripetal force works.
“Skaters must use their muscles to create centripetal force, which pulls objects towards the axis of rotation, keeping them on a circular path,” said sports scientist professor Deborah King. “If they relax, their arms and feet will want to keep moving straight and will get flung outward.”
The Biology of Skating
Why do men seem to be able to perform a triple Axel more successfully than women? The answer is not that men are naturally better skaters or physically stronger than women. The difference is weight. Women skaters generally do not weigh as much their male counterparts. Without this extra weight, women cannot typically generate enough force to complete a triple Axel. So how did Nagasu do it?
Women use extra training and effort. Since Nagasu could not rely on extra body weight, like male skaters do, she had to work even harder. It was only through special training that she had the power and endurance to accomplish the jump.
As part of her training, Nagasu used a special piece of equipment called a skating harness. When they are buckled into this harness, skaters learn how to practice pulling in and tightening their bodies without skates on their feet. Away from the ice, they can instead focus on how to best hold their bodies to maximize centripetal force.
When an ice skater begins the Axel, he or she skates backwards. Then, the skater steps forward on the outer edge of one ice skate and leaps into the air. After completing the triple Axel, a skater can land back on the ice with a force more than four times his or her body’s weight. In addition, all of that force is concentrated on a thin ice skate blade that is only a quarter-inch thick. Put another way, since Mirai Nagasu weighs 125 pounds, she must be strong enough to endure 500 pounds of force when she lands a triple Axel!
Because of these forces, skaters have to pay attention to everything that they are wearing in a competition. For example, when creating Nagasu’s Olympic dress, costume designer Pat Pearsall had to consider the weight of everything used to create it.
“We are keeping in mind the weight of the stones, the weight of the dress, and something that people never think about is the weight of the glue,” Pearsall explained. “That is a consideration in her dresses probably from this point forward.”
Centripetal force challenges the body in yet another way. In order to complete a triple Axel, a skater must spin very quickly in the air—three-and-a-half times in less than one second. Spinning so quickly makes it difficult to breathe right at a time when a skater is exerting his or her body so strongly.
“The faster you spin, the harder it is to breathe because there is so much force, and you have to stay controlled,” Nagasu explained.
After completing the triple Axel, Nagasu understandably feels very proud of her accomplishment. She said,“It’s not a jump that the others can do, so I take pride in that. I’m super proud that I’m going down in history.”
Images and Sources
Centripetal force diagram: Brews Ohare
Centripetal force diagram license: Public domain