Science Friday

The Surprising Science Of Why Sneakers Squeak

March 9, 2026

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  • The squeaking sound of basketball shoes is caused by supersonic slip pulses, or wrinkles, traveling across the frictional interface between the shoe sole and the court surface. 
  • The dynamics of shoe squeaking share surprising similarities with geophysical phenomena like earthquakes, leading the researchers to coin the term "shoequake." 
  • Electrostatic discharge, or "shoe lightning," resulting from the charge imbalance created by rubbing the shoe on the surface, can trigger these slip pulses that cause the squeak. 

Segments

Introduction and Motivation
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(00:01:09)
  • Key Takeaway: Physicist Adel Djellouli was motivated to study sneaker squeaks after observing the constant noise at his first NBA game.
  • Summary: Host Flora Lichtman introduces the topic of the surprising science behind basketball shoe squeaks, noting the physics involves lightning bolts and earthquakes. Guest Dr. Adel Djellouli explains that his curiosity was driven by the omnipresent sound at a Boston Celtics game. He emphasizes that even simple questions can be scientifically deceptive.
Experimental Setup and Observation
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(00:03:13)
  • Key Takeaway: A specialized optical setup using total internal reflection visualized the contact interface between the shoe and the floor.
  • Summary: Djellouli borrowed a beat-down basketball shoe for the experiment to avoid purchasing questions from grant administrators. The setup involved an acrylic plate, LEDs, and a high-speed camera synchronized with a microphone to visualize contact loss. Contact with the surface appeared bright, while loss of contact resulted in darkness.
Discovery of Slip Pulses
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(00:05:15)
  • Key Takeaway: Shoe sliding is not uniform; it involves supersonic slip pulses, or wrinkles, traveling across the interface.
  • Summary: High-speed imaging revealed that the shoe sole wrinkles, and these wrinkles travel at supersonic speed. The frequency of these fast-traveling wrinkles determines the frequency of the squeaking sound. This motion is characterized by slip pulses where the interface is stuck except for the regions where the wrinkle propagates, similar to shaking a rug.
Geophysical Parallels
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(00:07:03)
  • Key Takeaway: The supersonic slip pulses observed in shoe friction are phenomena typically seen in geophysical settings like earthquakes.
  • Summary: Seeing supersonic slip pulses was exciting because rubber tribology is usually considered boring and slow. The dynamics of the rupture during a shoe slide share similarities with continental plates sliding against each other during an earthquake. Djellouli humorously suggests this phenomenon could be called a “shoequake.”
Discovery of Shoe Lightning
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(00:08:18)
  • Key Takeaway: Lightning, or electrostatic discharge, was systematically observed as a trigger for the opening slip pulses during shoe sliding.
  • Summary: Reviewing the high-speed footage revealed systematic lightning events that triggered the slip pulses, initially mistaken for camera glitches. Rubbing two objects creates an imbalance in electric charges, and when this potential is sufficient, it discharges to equilibrate. This mini-explosion drastically increases local temperature and pressure, initiating the slip pulses.
Universality of Squeaking Physics
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(00:12:03)
  • Key Takeaway: The squeaking phenomenon is not limited to rubber shoes but also occurs when sliding human skin across a smooth surface.
  • Summary: Researchers tested if the effect was universal by sliding a hand on a smooth mirror, which produced a high-pitched hissing sound. Imaging the hand sliding on acrylic showed “handquakes” traveling at hundreds of meters per second and repeating tens of thousands of times per second. This confirms the underlying physics applies to various sliding interfaces.
Conclusion and Artistic Expression
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(00:12:53)
  • Key Takeaway: The research process was characterized by challenging assumptions, stubbornness, and culminated in creating music using squeaking rubber blocks.
  • Summary: Djellouli described the research as a scientific ‘acoupoirot story’ requiring constant challenging of assumptions and perseverance. The team created a squeaky rendition of Darth Vader’s Imperial March, which took three days to rehearse due to the coordination needed to achieve the proper tempo and notes.