The true nature of the 'squeak' sound in the gymnasium has been scientifically explained; it turns out that it's not just a sound, but also a tiny thunderclap.
The 'squeak' sound of gym shoes rubbing against the floor is a familiar memory for many people from their youth. It's also a sound often heard in basketball game footage. A research team from the John A. Paulson School of Engineering and Applied Sciences at Harvard University has uncovered the mechanism behind this sound.
Squeaking at soft–rigid frictional interfaces | Nature
The Physics of a Squeak
https://seas.harvard.edu/news/physics-squeak
The 'squeak' sound of shoes is a common phenomenon in everyday life, but the physical properties between rigid and soft objects like 'shoes touching the floor' have not been fully elucidated, and the cause of the sound was unknown. Therefore, the research team combined a high-speed camera capable of shooting 1 million frames per second, a total internal reflection fluorescence microscope (TIRF) , and acoustic measurements to observe the physical properties of the soft rubber of a shoe sole rubbing against the hard glass.
Here's what the experiment looked like: A rubber shoe sole was rubbed against the glass surface.
The results of the experiment revealed that when a shoe sole slides across a glass surface, the amount of friction fluctuates periodically, a phenomenon the researchers call 'open slip pulses.'
The research team found that the squeaking sound is produced by the release slip pulse, and that the pitch of the sound is determined by the pulse period. They also found that the pulse period depends on the shape of the sole of the shoe, meaning that the pitch of the sound can be adjusted by changing the shape of the sole.
The research team has released a video showing how different rubber blocks can be used to play the Imperial March (Darth Vader's theme).
An unexpected finding was the generation of tiny lightning bolts when the soles of the shoes rubbed against the glass surface.
You can see the lightning being emitted from the sole of the shoe from around 51 seconds into the video below.
Squeaking at soft-rigid frictional interfaces: lightning - YouTube
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