Tennis Balls with Spin Travel Less Far than Those without Spin

Jue Gong

Overview

A defining, yet complicated aspect of tennis is the spin. It was evident that spin greatly alters trajectory after impact, but spin had also been identified to affect aerodynamics in flight. In fact, the Magnus Effect states that spinning causes an unbalance of pressure around the ball, generating a net lift force. This phenomenon can possibly influence all tennis players—from professionals known for their tactical shots, to beginners that have trouble adjusting to the flight of spinning balls. Most previous studies had only analyzed a spinning ball’s aerodynamic coefficients in wind-tunnels, and a direct relationship between spin and tennis-play is generally a qualitative observation. Therefore, this paper sought to quantify the effect of increasing spin rates on the trajectory displacements in real tennis-play. In the experiment, 100 shots were launched with a ball machine and filmed overhead at an indoor tennis court for spin rates of 0, 450, 950, and 1400 rpm. The locations of the first bounces were identified via frame-by-frame video analysis. The trajectory displacements were calculated based on reference points and lengths using image-processing softwares. After data analyses, statistical analyses revealed that increasing the spin rates did significantly decrease displacement. Therefore, the results can be applied in tactical shots or in teaching beginners to understand ball placements. Ultimately, this study verified the significance of the Magnus Effect in real-life tennis, suggesting the possibility of additional investigations in engineering.

My Story

The inspiration behind my project originated back in freshman year, when I began playing tennis at my high school. It was my first tennis season ever, and I couldn’t have been more excited. However, I soon discovered that tennis was not as straightforward as I expected. Balls with spin were especially challenging, not only because they bounced so fast, but also because they seemed to swerve in flight.

This apparently unnatural phenomenon was baffling and yet intriguing. Through some background research, I found out that this effect goes all the way back to Isaac Newton's time, when he noticed it while watching tennis players at Cambridge! It turns out that this deflection is a natural behavior in spinning objects—spinning changes the airflow, which can alter aerodynamic forces. So I wondered, what can I do with this theoretical effect to improve my understanding of tennis? What I decided to do was to examine whether topspin will significantly change ball trajectories, uniting physics, tennis, and potentially engineering.

All parts of this project, from experimenting with the ball machine, to putting (a lot of) tape on the tennis court, were gratifying. I also learned to be flexible after multiple obstacles (I somehow reasoned at first that I could film an entire tennis court overhead with my iPhone). However, these challenges made it more rewarding! This project has helped me start looking more into the practical, non-sport applications of my results, and I am excited to cook up new engineering projects in the future!