Why Petting Your Cat Leads to Static Electricity

Petting a cat or shuffling across carpets often leads to static electricity. Although this phenomenon puzzled researchers for over two millennia, Northwestern University scientists have now revealed its mechanics.

Researchers discovered that sliding objects experience varying forces at their front and back. This force difference causes distinct electrical charges to accumulate on each part. The resulting charge imbalance creates a current, resulting in that notorious light zap.

This study appears in the journal Nano Letters. Laurence Marks, a professor emeritus of materials science and engineering at Northwestern, led the research team. "For the first time, we can explain a mystery that has baffled many: the mechanics of rubbing materials," he said.

Previously, attempts to explain the phenomenon faltered, relying on unjustified assumptions. Marks noted, "Now we can explain it simply. Different deformations at the front and back of a sliding object create current based on their differing charges."

Karl Olson, a Ph.D. student in Marks' group, is the first author of the paper. The quest to understand this mystery began in 2019. They identified that rubbing two surfaces causes small protrusions to bend, which generate voltages.

"In 2019, we uncovered the foundational aspect; it was just a seed," Marks explained. "Now, like a blossomed flower, we created a model that calculates electrical current. Our values aligned well with experimental data."

The key concept behind this model is "elastic shear." This occurs when a material resists sliding. For instance, when sliding a plate across a table, it resists motion, creating friction and subsequently moving electrical charges.

Marks emphasized, "Sliding and shear are closely connected."

While static electricity can create amusing situations, like hair standing on end after a slide, it can lead to serious dangers. Sparks from static have caused industrial fires and even explosions. Additionally, static discharge can disrupt the accurate dosing of powdered pharmaceuticals. Improved comprehension of these mechanics may enable researchers to devise solutions to these issues.

Marks remarked, "Static electricity impacts everyday life significantly. Charging grains with static significantly affects how coffee beans are ground and their flavor. Moreover, static electricity plays a crucial role in the planet formation process, connecting colliding grains via electrical interactions. It’s fascinating how significantly our lives and the universe rely on static electricity."

Earlier, SSP told about why dogs stare intently at us.