Freshly Baked Science
The Physics of Figure Skating
23rd December 2018
Figure skating is an unbelievable sport and takes a lot of skill and experience to master. Once mastered, the outcome is breath-taking and can produce some incredible performances. Figure skaters rely on science to make sure they glide across the ice and remain upright and even more so during their tricks and turns.
The main element of figure skating is balance. Without balance, the figure skater would end up on the floor in an extremely ungraceful manner. Remaining balanced throughout twists, tricks and turns requires the skaters centre of mass directly over the point in contact with the ice. The centre of mass of regular shaped objects like a cube or sphere is very easy to find, but on irregular shapes such as the human body, it can be harder to find. A person’s centre of mass if highly variable, as people carry their weight in different areas, but in most people, it will be just below the navel. Throughout an entire performance, the skater much ensure that their centre of mass is directly over whichever foot is on the ice to make sure they stay fully balanced.
During spins, the skater will have to think about their ‘moment of inertia’. This is the distribution of mass relative to the centre of mass. While spinning, if the skater wants to spin faster, they pull their arms in to reduce their ‘moment of inertia’ by decreasing the mass distribution. If they want to slow their spin down, they put their arms out to increase their ‘moment of inertia’ by increasing the mass distribution.
This takes us on to jumping spins, which relies on 3 different factors: the angular motion when they leave the ice, how small they can make their ‘moment of inertia’ and how long they spend in the air. Any slight changes in position while in the air can make an enormous difference and alter the speed of rotation. It’s quite a vicious cycle for figure skaters who are trying to pull off triple or quadruple spins as to increase their air time they need jump higher, so will need more strength. When they gain strength they will also gain muscle mass, the extra muscle mass will increase their moment of inertia and slow them down in the air.
Some physicists have looked into the possibility of completing a quintuple jump spin, but most believe it would be impossible. Carrying out a quadruple jump takes the smallest possible moment of inertia and jump height. If a quintuple was strived for, they would need to surpass their maximum jump height, get more angular momentum and decrease the moment of inertia even further!
Being a figure skater relies on being comfortable with knowing your own centre of mass and being able to maintain it through complex tricks and contortions. A figure skater must also stay quite slight to be able to reduce their moment of inertia sufficiently to increase their rotation speed and stay agile on the ice.
We’d love to see videos of you ice skating this winter! Send them in to us at firstname.lastname@example.org or via social media (@wonkscience) with the hashtag #STEMintoChristmas!