The screeching sound that Scotch tape makes when you rip it off a surface -- that fingernails-on-a-chalkboard noise most people try not to think about -- is produced by shock waves from micro-cracks that travel across the peeling tape at supersonic speeds, according to a new paper published in Physical Review E. Researchers led by Sigurdur Thoroddsen of King Abdullah University in Saudi Arabia used simultaneous high-speed imaging and synchronized microphones to capture both the propagating fractures and the sound waves they generate in the surrounding air. The team's earlier work, in 2010, had identified a sequence of transverse cracks racing across the width of the adhesive during peeling, and a 2024 follow-up established a direct correspondence between those cracks and the screeching sound, but neither study pinpointed a mechanism. The new findings show that a partial vacuum forms between the tape and the surface as each crack opens, and because the crack moves faster than air can rush in to fill the void, the vacuum travels along until it reaches the tape's edge and collapses into the stationary air outside, producing a discrete sound pulse.

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