Tape screeches as it’s pulled off the roll—a distinctive sound that physicists have linked to cracks spreading through the adhesive at supersonic speed. To test this, researchers yanked at Scotch tape fixed to a 2-centimeter-thick glass plate held firmly in place. A high-speed camera, looking up from the bottom of the glass plate, captured how the cracks formed on the adhesive side as the researchers peeled the tape. Another ultrafast camera recording at an eye-popping 2 million frames per second looked for shock waves in the air by detecting how those ripples, which change the density of the air, bent the otherwise parallel light beams from two concave mirrors. Starting at one edge, the cracks traveled along the width of the tape, with typically many of them moving in the same direction in rapid succession. The researchers did not see any shock waves in the air as the cracks formed and propagated across the width of the tape, which negated their original hypothesis. However, when the cracks reached the other edge, they let out a train of sharp shock waves. “The microphone closer to the end-point of the crack saw the sound pulse first,” the authors write in the study. The cracks moved at supersonic speeds—that is, faster than the speed of sound in the surrounding air—which was crucial to the screeching sound they produced. As a crack formed, air rushed in to fill the space. However, the authors write, “The crack moves too fast for this void to be filled immediately.” Consequently, the voids are only partly filled with air and have low air pressure. The faster the cracks moved, the larger the voids they left in their wake. “What we hear when we peel tape is these low-pressure voids collapsing into the air around the tape when the cracks reach the edge,” says Anastasiia Krushynska, a materials scientist not involved in the study. A better understanding of the mechanics and acoustics of peeling tape could lead to a quieter tape. Although it is merely an annoyance to most of us, the sound of peeling tape is a constant nuisance for workers in the shipping and packaging industry. Learn more: https://scim.ag/4oXlM7A FOOTAGE CREDIT: LI ET AL./PHYSICAL REVIEW E #NewsFromScience #Science #ScienceShorts