SCOTT SIMON, HOST:
The question every basketball player must consider, from the pros to kids shooting hoops on a driveway, is, what shoes do you wear?
BRANDON SHERROD: What I look for in a basketball shoe, No. 1, is stability. The second thing that I look for is style - look good, play good. The third thing is, honestly, does it squeak?
(SOUNDBITE OF SHOES SQUEAKING)
SIMON: Brandon Sherrod is an assistant coach for Yale's basketball team, and he appreciates the squeak.
(SOUNDBITE OF SHOES SQUEAKING)
SHERROD: I do think it's fair to say that if your basketball shoes aren't squeaking, you're not working hard.
SIMON: Harvard physicist Adel Djellouli also loves the squeak but for scientific reasons. He's been listening carefully to the squeak since 2021.
ADEL DJELLOULI: Celtics was playing - if I remember well - it was the Bucks. The one sound that is omnipresent is their shoes squeaking. So it was something that was not familiar to me, but it got my wheels spinning, and I decided to look at what's going on under the shoe.
SIMON: Adel Djellouli is on the team of scientists who recently demystified what causes that shoe squeak. Scientists previously thought it came from a phenomenon known as stick-slip.
DJELLOULI: Think about stick-slip as your mug on the table, right? So when you drag your mug on the table, you will alternate between periods where it's completely stuck and periods where it's moving.
SIMON: So their scientific team experimented.
DJELLOULI: We isolated the system by taking that shoe and then reimagining it into a rubber block. So the interface is flat, and then you rub it on a smooth surface, dry, at high speeds.
SIMON: And...
(SOUNDBITE OF SCRAPING NOISE)
DJELLOULI: There is no note. There's just noise. It's very similar to when you open tape - right? - and it makes this (imitating tape dispensing) sound.
SIMON: That's called broadband noise. It's not a squeak. Then Djellouli wondered what would happen if you add a pattern or ridges?
DJELLOULI: The moment you slide it, you get a note.
(SOUNDBITE OF HIGH-PITCH PULSING NOISE)
SIMON: Using high-speed cameras, he discovered that only a small part of each ridge separated from the ground at any given time. A pulse traveled down the ridge thousands of times per second, riling the air around it and producing the squeak.
DJELLOULI: These type of pulses - they mimic earthquakes. So your shoe is basically having shoe quakes several thousands of times per second.
SIMON: Djellouli says that the pitch of the squeak depends on the height of the sole, and delighted by their finding, the team of scientists tried to make actual music.
DJELLOULI: Since we're all a bit nerdy, and we decided to go for Darth Vader's "Imperial March."
(SOUNDBITE OF SHOE SQUEAKING MELODICALLY)
DJELLOULI: And we had to rehearse for three days until we got something that is somewhat decent, although slightly out of tempo.
SIMON: Beyond the soles of shoes and music, Djellouli says, their findings might help us better understand Earth's tectonic plates.
DJELLOULI: Why do earthquakes begin at a given moment? What triggers them? What is the rate of repetition? Can we find order in that chaos?
SIMON: No answers yet for predicting earthquakes, but what about that other pressing question - what basketball shoe squeaks best?
DJELLOULI: Man, there are different basketball shoes that we liked throughout this study, but I'm with the classics. I go back to the Jordans.
SIMON: But whatever shoes you choose, remember, you're wearing a musical instrument.
(SOUNDBITE OF SHOES SQUEAKING) Transcript provided by NPR, Copyright NPR.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.
