The high-pitched sound of shoes scraping across a gymnasium floor is familiar to every basketball fan. Long considered to be the simple result of friction between the sole and the ground, this phenomenon actually hides complex mechanics. A study published in the journal Nature shows that the frequency of this squeaking directly depends on the shape of the grooves in the sole.
Researchers found that the geometry of the sole pattern influences how the surfaces grip and then slide over each other. This mechanism produces repeated sliding pulses, the frequency of which will determine the noise. Thanks to this discovery, the team even managed to design silicone blocks capable of playing a specific note.
Replay the “Imperial March”
Relayed by Ars Technica, this study was carried out by physicist Katia Bertoldi of Harvard University and published at the end of February 2026. The scientist and her team were interested in the phenomenon called “stick-slip”, a cycle where phases of adhesion and sliding alternate between two surfaces in contact. This principle is at the origin of other acoustic phenomena observable in everyday life, such as that of tires screeching on the road.
But the case of sports shoes is particular: it is the result of contact between a flexible material and a rigid surface, whereas the phenomenon studied until now was based on the interaction between two rigid materials. The researchers therefore wanted to understand how this interaction worked.
To do this, they slid basketball shoes across a smooth, dry glass plate, recording the images and sounds produced at the contact level. Analyzes revealed that separation waves formed very quickly between the sole and the surface, which is the source of the acoustic pulses causing the squeaking.
The scientists then replicated the experiment with lab-designed silicone blocks, some with a smooth surface and others with parallel grooves similar to those on the soles of basketball shoes. Above a certain speed, both types of silicone produced sliding pulses, although there was a notable difference in the sound produced. The smooth blocks actually generated a diffuse and irregular noise, like a breath, while the grooved blocks produced a much more stable and identifiable frequency sound.
By changing the height and spacing of the grooves, the researchers were able to precisely control the frequency of the sound. They even managed to create blocks each corresponding to a specific note, which allowed them to play for the famous “Imperial March” of Star Wars as a demonstration.
Beyond the anecdote, this discovery could have important applications. Understanding how to adjust frictional properties could help design materials that can move from a very sticky state to a more slippery state as needed. The researchers also point out that the observed dynamics resemble those of tectonic faults during an earthquake. The squeaking of a sole could thus serve as a simplified model to study the propagation of geological ruptures.
