Researchers led by Er Qiang Li at the University of Science and Technology of China have identified supersonic fractures within the adhesive layer as the primary source of the sound produced when cellophane tape is peeled. The investigation, which utilized ultra-high-speed cameras and sensitive microphones, concluded that the sound is generated by a series of weak shockwaves that form when these rapid fractures reach the tape's edges.
Background on the Phenomenon
The sound emitted by peeling adhesive tape has been a subject of scientific inquiry for decades. Earlier research offered various hypotheses. A 2010 study proposed that elastic waves traveling up the detached tape might be responsible for the sound. Subsequently, a 2014 paper linked the sound to fractures within the tape but did not fully elucidate the exact mechanism behind the sound generation.
Experimental Observation
Li's team conducted experiments observing a 19-millimeter-wide strip of ordinary transparent Scotch tape being peeled from a glass surface. The peeling process was monitored using two high-speed cameras, including a schlieren imaging system, and two sensitive microphones. This setup allowed for precise observation of the tape's detachment and associated air disturbances.
The researchers confirmed that tape peeling exhibits a 'stick-slip' behavior, characterized by the adhesive temporarily clinging before suddenly giving way under pulling force. During each 'slip' phase, the adhesive does not detach uniformly. Instead, it tears in narrow bands, identified as transverse fractures, that rapidly race sideways across the tape's width.
Mechanism of Sound Generation
The core finding of the study was the speed of these transverse fractures. Measurements indicated that these fractures moved at speeds ranging from approximately 250 to 600 meters per second. Some fractures were observed to travel at speeds nearing twice the speed of sound in air, which is approximately 342 meters per second.
As these high-speed fractures propagate, they create a momentary gap, forming a partial vacuum, between the tape and the glass surface. When these vacuum pockets reach the tape's edge, air rapidly rushes in to fill the void. This rapid influx of air causes an abrupt collapse of the cavity, which in turn generates weak shockwaves.
These shockwaves were measured propagating at approximately 355 meters per second, slightly exceeding the speed of sound in air.
Confirmation and Conclusion
To confirm the origin of the sound, researchers compared the arrival times of the sound at two different microphones. This analysis verified that the shockwaves originate specifically at the tape's edges.
The study concluded that while elastic waves might contribute to the overall sound, the train of weak shocks generated by the collapse of vacuum pockets is the dominant mechanism responsible for the sound of peeling tape.
The findings of this research were published in the scientific journal Physical Review E.