Scotch tape has been a household mainstay for nearly a century, but it still holds some scientific surprises. Researchers have discovered that the screeching sound emitted when one rapidly peels Scotch tape—akin to the screech of fingernails on a chalkboard—is the result of shock waves produced by micro-cracks propagating along the tape at supersonic speeds, according to a new paper published in the journal Physical Review E.
It was a 3M engineer named Richard Drew who developed the first transparent sticky tape in 1930. The impetus came from car manufacturing, specifically two-color designs, where the adhesives used were so sticky they often removed the paint when peeled off; the paint then needed to be manually touched up. Drew found a sandpaper adhesive with just the right amount of stickiness and used it to coat a roll of cellophane tape. (Fun fact: Drew also co-invented the snail-style dispenser for the tape with his 3M colleague, John Borden.) The tape was hugely popular during the Great Depression; consumers used it to repair everyday items rather than replace them. That popularity has never waned.
Scotch tape has also generated considerable interest among physicists. Back in 1939, scientists noticed that peeling tape could produce light—specifically, a glowing line where the tape end pulls away from the roll. The phenomenon was first recorded in the 17th century and is known as triboluminescence: the generation of light when a material is crushed, ripped, rubbed, or scratched. Diamonds, for instance, sometimes glow blue or red during the cutting process, while ceramics emit yellow-orange light when being cut by abrasive water jets.
The most popular example is Wint-O-Green Life Savers: crush the candy in a dark closet and you can see the sparks produced. It’s the sugar crystals that produce the effect: the crushing action rips electrons from the molecules, which leap across the gap to the more positively charged side. The jumping electrons collide with nitrogen atoms in the air, which briefly absorb the energy and then emit UV light. The effect is made visible by the wintergreen oil used for flavoring, i.e., fluorescent methyl salicylate, which absorbs UV light and converts it into blue light.