Djellouli, a materials scientist at Harvard University, became focused on the sound after watching the Boston Celtics play at TD Garden. He said the squeaking—heard when players slide on the court—was “omnipresent” and that it is “always there.”
In the same context of rubber-on-hardwood friction, the study described how the squeak can be reproduced and measured under controlled conditions. Djellouli and colleagues repeatedly slid a sneaker against a smooth glass plate, capturing the squeaks with a microphone and filming the contact area with a high-speed camera to observe what happened under the shoe.
The Nature study, published Wednesday, describes a mechanism tied to grip. As the shoe works hard to keep its hold on the surface, the researchers reported that tiny sections of the sole repeatedly change shape as they momentarily lose and then regain contact with the floor thousands of times per second. They said the pulses created by that rapid contact switching match the pitch of the loud squeak.
The work also explored how shoe design can affect whether those friction events produce a distinct sound. In trials in which researchers slid blocks of flat, featureless rubber against the glass, they reported seeing chaotic, disorganized ripples but not hearing squeaks. The study attributes the emergence of the clear squeak in part to ridge-like designs on the shoe bottom, which the researchers said may organize the bursts into a high-pitched sound.
Djellouli summarized the explanation in terms of physical motion at the sole’s surface. “That squeaking is basically your shoe rippling, or creating wrinkles that travel super fast,” he said. He added that “They repeat at a high frequency, and this is why you get that squeaky noise.”
The research was framed as moving friction science closer to the speeds associated with sports. The study notes that other researchers have studied similar “bursts” before, but that this sneaker work examines friction at much faster speeds and, for the first time, links the speedy pulses to the squeaking sound.
In an editorial accompanying the research, physicist Bart Weber said friction remains difficult to predict and control despite its practical importance. “Friction is one of the oldest and most intricate problems in physics,” Weber wrote, and he added that “it is difficult to predict and control.” The article says better friction understanding could help with problems such as how Earth’s tectonic plates slide and grind during earthquakes, as well as efforts to reduce friction and wear to save energy.
The Nature study’s implications also extend to everyday court moments. The researchers said their findings do not provide an immediate fix, and they cautioned that popular internet advice—such as rubbing soap or a dryer sheet on shoe soles—may be risky. Still, the work suggests design routes toward quieter footwear: one additional experiment found that changing the thickness of the rubber can make the squeak sound lower or higher in pitch.
Weber, who is with the Advanced Research Center for Nanolithography and the University of Amsterdam, described that possibility as a new design start. “We can now start designing for it,” he said. “We can start making interfaces that either do it if we want to hear this sound, or don’t do it if we don’t want to hear it.”