In ancient Greece, philosopher Thales of Miletus noticed something strange. When he rubbed fur on amber, the amber attracted dust. This seemingly trivial observation was the first documentation of static electricity. For over 2,600 years, scientists have grappled with understanding what caused this strange effect in detail. Now, thanks to new research, we finally know the answer.

“For the first time, we are able to explain a mystery that nobody could before: why rubbing matters,” said materials scientist Laurence Marks of Northwestern University.

The key lies in how different deformations on materials during sliding create electric charges.

“People have tried, but they could not explain experimental results without making assumptions that were not justified or justifiable,” Marks added.

“We now can… Just having different deformations — and therefore different charges — at the front and back of something sliding leads to current.”

A Simple Solution to a Complex Puzzle

Static electricity occurs when two materials rub against each other, generating a charge transfer. This effect, known as triboelectricity, happens when tiny imperfections on the materials’ surfaces deform under friction. These deformations result in differences in electric charge between the front and the back of the sliding materials — something that Marks and colleagues figured out in a previous 2019 study.

Back then, they found that rubbing materials together created microscopic protrusions that generated voltage. This deformation is essential to the development of static electricity.

Now, the team has made a new breakthrough by developing a model that explains the core mechanism: elastic shear. Elastic shear describes how materials resist the sliding motion, creating friction. This friction builds up charges on different parts of the materials, producing a current — and ultimately, a static shock.

“We developed a new model that calculates electrical current,” Marks explained. “The values for the current for a range of different cases were in good agreement with experimental results.”

“Sliding and shear are intimately connected,” he added.

Why This Matters

Static electricity may seem like a trivial annoyance — think of the crackle when you brush your hair or the shock after touching a doorknob. But its effects go far beyond everyday life. Static electricity can create real hazards, particularly in manufacturing and industrial settings. Sparks from static buildup can cause fires, and static can even alter the flavor of coffee beans in grinders.

Marks notes that static electricity plays a role on a much larger scale. “The Earth would probably not be a planet without a key step in the clumping of particles that form planets, which occurs because of the static electricity generated by colliding grains,” the researcher added.

This research doesn’t solve every aspect of triboelectricity, but it provides a crucial piece of the puzzle. The ability to control and predict static electricity could have significant applications in fields ranging from medicine to aerospace, where small electric shocks can have big consequences.

Further experiments will help refine the details. Scientists hope that with time, they will fully understand triboelectricity and potentially find ways to prevent or control it in environments where it poses a risk. For now, after thousands of years, we finally have an answer to one of science’s oldest mysteries.

The findings were reported in the journal Nano Letters.