The Physics Behind Squeaking Sounds

Researchers uncover new insights into the mechanisms behind everyday squeaking noises.

Published on Feb. 26, 2026

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Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences, in collaboration with the University of Nottingham and the French National Center for Scientific Research, used high-speed imaging to investigate the dynamics of soft solids sliding rapidly on rigid substrates. They discovered that squeaking sounds are not produced by random stick-slip events, as previously thought, but rather by rapid, wrinkle-like detachment fronts that propagate along the interface at high speeds. The study also found that these opening slip pulses can trigger triboelectric discharges, or miniature lightning bolts caused by friction.

Why it matters

The findings from this study challenge the conventional understanding of friction and could lead to new ways to engineer and control advanced materials. Tuning frictional behavior on the fly has been a long-standing engineering goal, and this new insight into how surface geometry governs slip pulses paves the way for tunable frictional metamaterials that can transition from low-friction to high-grip states on demand.

The details

The researchers used high-speed optical imaging and synchronized audio measurements to directly visualize the contact interface between soft rubber and rigid glass. They discovered that sliding does not proceed uniformly, but rather localizes into rapid, wrinkle-like detachment fronts that propagate along the interface at high speeds. These opening slip pulses, not random stick-slip events, are what produce the audible squeak. The study also found that the squeak frequency is set by the repetition rate of these propagating pulses, and that the pulses can be triggered by triboelectric discharges, or miniature lightning bolts caused by friction.

  • The research was carried out in 2026.

The players

Adel Djellouli

A postdoctoral fellow in the lab of Katia Bertoldi at the Harvard John A. Paulson School of Engineering and Applied Sciences, and the first author of the study.

Katia Bertoldi

The William and Ami Kuan Danoff Professor of Applied Mechanics at the Harvard John A. Paulson School of Engineering and Applied Sciences, and the senior author of the study.

Gabriele Albertini

A researcher at the University of Nottingham and a co-author of the study.

Shmuel Rubinstein

A professor of physics at the Hebrew University of Jerusalem and a visiting professor at the Harvard John A. Paulson School of Engineering and Applied Sciences, as well as a co-author of the study.

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What they’re saying

“This project started with a simple question: why do basketball shoes squeak?”

— Adel Djellouli, Postdoctoral fellow (Nature)

“Tuning frictional behavior on the fly has been a long-standing engineering dream. This new insight into how surface geometry governs slip pulses paves the way for tunable frictional metamaterials that can transition from low-friction to high-grip states on demand.”

— Katia Bertoldi, William and Ami Kuan Danoff Professor of Applied Mechanics (Nature)

“We were surprised that tiny surface features could so strongly reorganize frictional motion. These results challenge the assumption that friction can be fully captured by simplified one-dimensional models and highlight the critical role of interface dimensionality.”

— Gabriele Albertini, Researcher (Nature)

What’s next

The researchers plan to continue exploring how the geometry and properties of materials can be engineered to control frictional behavior and the generation of squeaking sounds.

The takeaway

This study provides new insights into the physics behind everyday squeaking sounds, challenging the conventional understanding of friction and opening up new possibilities for engineering advanced materials with tunable frictional properties.