The Physics of The Biles

    Simone Biles is an incredible gymnast, who continues to shock the world with her ability to seemingly defy the laws of physics! I have always been fascinated by the world of gymnastics and how they are able to do such incredible movements with their bodies. Thus, when I was looking to investigate some physics phenomenon I was immediately drawn to gymnastics. When beginning to look into this I noticed a movement that seemed to draw on multiple concepts of the physics we have discussed this semester, a movement named after no other than Simone Biles. The Biles is a double half-layout with a half twist and a blind landing. This move is so shocking because at first glance it appears that Biles is actually gaining angular momentum, which we know is impossible because of the Law of Conservation of Momentum. In this movement she flips twice and then still has enough momentum to complete a turn and land facing the way she was running. In this movement, Biles utilizes everything from torque, to momentum, to kinetic energy and moment of inertia. Thus, I decided to look over the physics of this motion with the help of Sheffield Hallam University’s John Kelley and Cairan McInerney who analyzed Biles movement in 2016 after she successfully performed the move in an international event. 

     The first part to think about in this move is the idea of angular momentum, which is angular velocity times the moment of inertia. Thinking about this expression we known that the momentum must be conserved throughout the movement, thus if Biles wants to complete two flips with the same momentum she must theoretically increase her angular velocity in order to spin faster. Yet, spinning faster means she would need to decrease her moment of inertia in order to conserve momentum. In order to do this, similar to the ice skater problem we did in class she would need to decrease her radius. She does this by creating an arch in her body, decreasing her radius in the y-direction, as well as bringing her arms to her hips, which decreases her radius in the x-direction. 

 

    Another interesting thing to look at in this problem is looking at her energy.  On the floor gymnast are able to build up energy by running diagonally such that they can turn their horizontal kinetic energy into vertical and rotational energy. However, the sprung floor also plays a critical role in how gymnasts are able to utilize physics as because of Newton’s 3^rdLaw, which states that two objects will exert equal and opposite forces onto each other. This is because as the gymnast applies a force, by doing a cartwheel or flip, the sprung floor will provide, and equal and opposite force back up on the gymnast by over a greater duration of time. Thus, the gymnast’s force as well as the spring force will be store then released onto the gymnast to allow her to complete such incredible motions.

 

    In the article that I read, John Kelley and Cairan McInerney, also look at the amount of energy and force that Biles needs to exert in order to complete the movement and while the math and process is a little to long for this blog post the results are incredible. The ability to calculate these things provide Biles and trainers with valuable information about how she must execute the move in order to succeed. As I talk about in my other posts this is the work of sports engineers who use the power and understanding of physics and apply it to performance. This work continues to amaze and fascinate me and I hope to see more defying of physics by the Women’s US Gymnastics team in the upcoming Olympics! 

Works Cited: 

https://www.inverse.com/article/19429-2016-rio-olympics-simone-biles-gymnastics-physics-medal

https://plus.maths.org/content/simone-biles