Scotch tape screeches when you peel it. Everyone knows the sound, and no one thinks about it. The standard assumption is friction — the adhesive resisting separation, vibrating like a bow on a string.
Thoroddsen and colleagues, filming at extreme speed with synchronized microphones (Physical Review E, 2026), showed that the mechanism is something else entirely. When tape peels, a crack races sideways across the adhesive surface faster than the speed of sound. The crack opens a cavity between tape and surface that air can't fill because the void is traveling supersonically — faster than air can rush in. The empty cavity rides the fracture front all the way to the tape's edge, where it collapses into the surrounding atmosphere. That collapse produces a pressure pulse. Each pulse corresponds to one crack reaching the edge. String enough of them together and you get the screech.
Tape noise is a sequence of tiny sonic booms.
The supersonic part is essential. If the cracks propagated below the speed of sound, air would fill the void as it opened and there would be no pulse — just the quiet hiss of adhesive separating. The screech exists because the fracture outruns the medium. The sound is not a byproduct of the peeling. It's a signature of a specific velocity regime that the peeling happens to occupy.
This is the kind of physics that hides in plain experience. The crack speed, the air dynamics, the pressure-pulse mechanism — none of this is accessible to intuition. You hear the screech and think “sticky surface, vibrating.” The reality involves supersonic fracture mechanics and collapsing vacuum cavities, operating at scales and speeds that require high-speed cameras to observe. The everyday phenomenon and the physics are separated by a gulf of mechanism that casual observation can't bridge.
The general pattern: familiar phenomena often occupy extreme physical regimes that their familiarity conceals. The snap of a whip is a sonic boom — the tip exceeds Mach 1. The blue of the sky is Rayleigh scattering — selective wavelength-dependent radiation from atmospheric molecules. The warmth of the sun is nuclear fusion filtered through eight light-minutes of vacuum. In each case, the experience is mundane and the mechanism is extraordinary. Familiarity doesn't indicate simplicity. It indicates that the mechanism is so reliable that you've stopped noticing it — and the reliability hides the physics.