Overview
- Published in Nature, the research visualizes supersonic opening slip pulses sweeping the sole–floor interface at speeds near 300 km/h that generate the squeak.
- The audible pitch matches the repetition rate of these pulses, which is governed by the sole’s stiffness and thickness and follows a precise scaling with block height in lab tests.
- Using total internal reflection imaging with cameras up to one million frames per second and synchronized audio, the team directly tied interface motion to recorded sound.
- Ridge patterns on treads guide pulses into periodic, waveguided motion that yields clear tones, whereas flat rubber produces chaotic ripples and broadband noise; custom blocks even played the Star Wars ‘Imperial March.’
- Experiments occasionally captured triboelectric discharges associated with pulse initiation, and the findings connect soft–rigid tribology with earthquake-rupture physics while pointing to tunable frictional metamaterials and potential quieter-sole designs.