When basketball shoes squeak so loudly, easy to hear on TV while watching the WNBA because there's no crowd noise, do you ever wonder why they squeak?
I realize an overwhelming majority of you haven't considered that question. Don't leave; it's interesting, in a geeky way.
A Harvard University team, led by postdoctoral fellow Adel Djellouli, finally answered that question, and the answer turned out to involve high-speed waves, microscopic detachments, and even tiny flashes of light.
Djellouli and his team filmed a real basketball shoe sliding across a smooth glass plate with cameras capable of capturing 1,000 frames per second. That ultra-fast imaging allowed them to see what the human eye never could. Instead of simple friction between the rubber and the floor, the team observed rapid, wave-like ripples traveling through the sole at speeds up to around 186 mph.
Those waves caused tiny sections of the rubber sole to lift off the surface and then snap back down thousands of times per second. Each snap pushes air outward, creating a pressure pulse. Stack enough of those pulses together, and you get the sharp, high-pitched squeak—close to the sound of Ilhan Omar protesting—that echoes through arenas during a fast break.
The frequency of those repeating waves determines the pitch of the sound; thicker or stiffer soles change how quickly the waves repeat, shifting the sound higher and lower. Smooth rubber soles produce irregular pulses that sound more like a dull swish. Grooved basketball treads act as guides, organizing the ripples into a steady rhythm and producing the clean squeak we all know and love.
Katia Bertoldi, William and Ami Kuan Danoff Professor of Applied Mechanics at the Harvard School of Engineering and Applied Sciences, co-led the study. Watching a Boston Celtics game, Djellouli first became curious about the noise, and what began as a mild annoyance turned into a serious research project.
The team combined total internal reflection imaging with ultra-fast video to see the real contact area between the shoe and the surface. The footage revealed small rubber patches buckling, detaching, and reattaching in organized bursts.
A material scientist at the University of Nottingham, Gabriele Albertini, contributed to the analysis and helped explain how tread patterns turn chaotic friction into something almost musical. To me, that music sounds like a merging of a gurgling cat and Yoko Ono singing.
Some researchers even detected tiny sparks in some trials when rubber snapped back into contact, flashes resembling miniature lightning bolts, caused by rapid electric discharge as the material separated and reconnected.
The waves traveling through the sole move so fast that they qualify as supersonic within the rubber, sweeping across the shoe in fractions of a second and repeating at frequencies near 4800 hertz, matching the "musical" pitch fans hear during sharp cuts and pivots.
Understanding those detachment waves has implications beyond sneakers. Similar frictional mechanics occur in car tires on wet pavement and even along earthquake faults, where tectonic plates slip. The same rapid release and reattachment process governs much larger forces in nature.
Engineers now have concrete data showing how sole thickness, stiffness, and tread geometry shape both grip and sound. Manufacturers could design shoes that reduce noise in gyms or tune models to deliver the feedback players rely on during quick defensive slides.
The team of Djellouli, Bertoldi, Albertini, and more, transformed an everyday sports noise into a serious study of friction physics. A single squeak on hardwood opened a window into hidden wave mechanics that work far beyond the baseball court.
So, the next time you're riveted watching an WNBA playoff game, where the squeaks are louder than the crowd, that won't be a random sound. It represents supersonic rubber waves, microscopic detachments, and physics happening in real time beneath every pivot.
