Overview
- An international team led from Harvard reports in Nature that sneaker squeaks arise from rapid, wave-like slip pulses at the rubber–surface interface.
- Using total internal reflection imaging and cameras running up to about one million frames per second, researchers directly linked evolving contact patterns to the audible tone.
- Ridged tread acted as a waveguide that confined pulses and produced a clear pitch, whereas smooth rubber generated irregular, broadband noise.
- The squeak’s pitch matched the pulse repetition rate set by sole thickness and stiffness, enabling the team to program specific musical notes in the lab.
- Experiments also captured occasional triboelectric discharges that can trigger pulses, pointing to ways to tune frictional noise and offering a laboratory analogue for fast rupture processes relevant to earthquakes.