Every child has experienced the magic of static electricity. Eyes light up as he or she performs magic by rubbing a balloon against his or her hair and the balloon then sticks to the wall.

Static electricity is, in actuality, an imbalance of electric charges with the surface or on the surface of a material. The charge remains where it is until it able to move away through an electric current or electrical discharge.

While a spark of static electricity can have a measurement of thousands of volts, it actually contains only a small current and only lasts for a brief period of time. Consequently it has little energy or power. While lightning is a powerful example of static electricity, over 70% of people struck by lightning survive. Static electric builds up faster on dry non-humid days. It also resulted in metal fences emitting electrical charges and the electrical systems in cars shorting out. In response, many people started carrying metal chains to counter the static charges.

Knowledge of the phenomenon of static electricity has existed for more than 2,500 years. Thales of Miletus found static electricity as he was cleaning his amber. However, little attention was paid to the phenomenon and no research occurred. Otto von Guericke created the first friction generator in the 17th century. Later Coulomb and Faraday conducted further research. Benjamin Franklin made the connection between static electricity and storms. However, throughout all this time no one has truly gained an in depth understanding of the process behind static electricity.

According to the article “Solving the Longstanding Mystery of How Friction Leads to Static Electricity”, a research team from Northwestern University has created a model which demonstrates that static electricity is produced by the bending of tiny asperities on the surfaces of two objects being rubbed together.

All materials, no matter how smooth they seem to be, actually have rough surfaces covered with an indeterminate number of tiny, minute asperities. As the two surfaces rub against each other, these asperities bend and become deformed. The research team determined that it is these deformities that create the voltages, which then cause static charging, or static electricity. This is the flexoelectric effect, which happens when charges are separated.

The research team created a Hertz based model that clearly showed that the voltages that occurred due to the bending and deforming of the surface features are strong enough to cause static electricity. The work also helps explain why electrical charges are created when two objects made of the same material are rubbed together.

The findings indicate that the three forces of triboelectricity, flexoelectricity, and friction are interrelated. Triboelectricity is the electric charge created by friction, or the electrification of different objects and materials due to the collision of electrons flowing from one material to another. The triboelectric effect refers to the process of rubbing different objects or materials against each other to increase surface contact in order to produce an electric charge. Flexoelectricity is the response of polarization due to the strain gradient. Friction is the resistance to motion of one object in relation to another object, or the created when two surfaces slide against each other. Friction is not a fundamental force, but is the result of an electromagnetic attraction between the charged particles existing in the two contacting surfaces. Researchers believe that the findings will allow for greater insight of how to handle these forces in new technologies.

Furhter information: Does Flexoelectricity Drive Triboelectricity?, C. A. Mizzi, A. Y. W. Lin, and L. D. Marks, DOI:https://doi.org/10.1103/PhysRevLett.123.116103.