Figure Skater: Physics on Ice

Recently, in Pyeongchang, South Korea, the 2018 Winter Olympic Games concluded following a closing ceremony packed with culture and athletes. Over two weeks of international competition, the world witnessed many moments that will be remembered as the highlights of another Olympic games.

According to online data found herefigure skating remains one of the most popularly searched topics relating to the Olympics.

A high-profile winter sport, figure skating mesmerizes with its ability to seemingly transcend physical constraints.The ease with which skaters glide across the ice reveals little of the strain involved in completing gravity-defying jumps, spins, and lifts. Figure skaters learn to twist to their advantage the same principles of physics that make their sport challenging.

Center of Mass

Center of mass, defined as the point representing the average position of the skater’s body mass, dominates aspects of skating. For skaters, the center of mass usually lies in the hips. While skating, the center of mass must be kept in line with where the skater’s blade contacts the ground. This region of contact is also known as the point of support. The weight of the skater’s mass rests on it, and the skater depends on it to stay upright.

The quarter-inch-wide blade of a figure skate provides a much smaller point of support than a normal shoe made for walking. This makes it easier to wobble in them, as the support for the body’s weight is concentrated in much smaller regions. If the center of mass shifts off the point of support even slightly, the skater will struggle to balance. The challenge of balancing is what makes ice skating so difficult for many people, especially beginners. Initially, the inability to move freely on the ice comes from inexperience in balancing the body’s center of mass over the thin blades acting as the point of support. Any movement across the ice causes imbalance and feels precarious.

Credit to the following: http://ftw.usatoday.com/2018/02/why-alina-zagitovas-win-over-evgenia-medvedeva-was-so-surprising

Even for advanced skaters, the center of mass adds difficulty to specific moves in other ways. For example, well-known figure skaters like Evgenia Medvedeva and Alina Zagitova frequently perform jumps with one or both arms over their head. These jumps employ greater technical difficulty due to the change in where the mass of the arms is located. Raising the arms shifts the skater’s center of mass from the hips to the upper chest, making it harder for the skater to rotate in the air and land cleanly.

Linear Velocity

Credit to the following: https://www.thoughtco.com/top-basic-figure-skating-jumps-1282930

Velocity factors into a figure skater’s performance as well. Velocity is composed of both speed and direction and describes either motion in a straight line (linear) or in rotation (angular). Linear velocity enables leaps and jumps off the ice. For example, the skaters push down on the ice with their blade and, in response, the ice pushes up on the skate with the same strength as the force of the blade. Newton’s third law of motion predicts this relationship between the force on the blade and ice – equal in strength but opposite in direction. The force pushing on the skater from the ice has acceleration, which causes a change in the skater’s vertical velocity. With the boost of vertical velocity, the skater launches upward into their jump.

Angular Velocity and Angular Momentum

Spins on the ice involve angular velocity. During spins, figure skaters extend their arms outward initially, before later drawing them in. This increases the speed at which skaters rotate. Angular momentum describes a rotating object’s tendency to continue in angular motion. Angular momentum depends on two things: the moment of inertia, which is mass in relation to the axis of rotation, and angular velocity. In addition, for objects not affected by any outside forces, the total angular momentum must remain unchanged.

Credit to the following: http://ffden-2.phys.uaf.edu/webproj/211_fall_2014/Ariel_Ellison/Ariel_Ellison/home.html

When a skater brings the arms closer to the axis of rotation (the center of the body), body mass concentrates near the axis. The moment of inertia, which quantifies the difficulty of rotating an object, decreases as a result. The effect of mass on angular momentum reduces as well. To conserve momentum after the decrease due to mass, angular velocity must increase. The skater, gaining additional rotational speed from the velocity, then begins to rotate faster.

Further Directions

Figure skating challenges athletes to push the limits of the human body, while also demanding artistry and grace. Some people even theorize that modern skaters are nearing the greatest amount of turns, rotations in the air, or speeds physically possible (read more here). The sport, ever-developing in style and technique, serves as a striking example of the fundamental scientific laws underlying motion.

 

Other Sources:

https://science360.gov/obj/tkn-video/11795e13-f6de-4334-a57a-dab7a90383ab/science-olympic-winter-games-figure-skating-physics

Edited by: Briana Fannin

Cindy Xie

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