Since ancient times, it has been known that after friction, small objects are attracted to each other or, conversely, are repelled. Centuries ago, scientists discovered that electrical charges were responsible. But physicists still argue about why rubbing bodies are charged. But recently, experts have finally found the answer.
The new version, which is in excellent agreement with the experimental data, is described in a scientific article accepted for publication in the journal Physical Review Letters. In the meantime, you can familiarize yourself with its preprint. The research was led by Laurence Marks of Northwestern University in the United States.
The first mention of electrification by friction is associated with the name of the ancient Greek philosopher Thales of Miletus, who lived in the 7th-6th centuries BC. He noticed that the fur, rubbed with an amber stick, attracts specks of dust. By the way, the ancient Greek word "electron" (ἤλεκτρον) literally means "amber".
Until now, physicists have not been able to reliably establish what mechanism is behind the electrification by friction, also called the triboelectric effect in scientific circles.
The new theory links it to the flexoelectric effect. This phenomenon occurs when a dielectric is subjected to uneven deformation (that is, the degree of deformation varies from point to point), a potential difference arises in it. This is due to the fact that electric charges are redistributed inside the substance.
Meanwhile, even the smoothest surfaces at the nanoscale are an unimaginable chaos of "mountain ranges" and "depressions". When rubbed, these tiny irregularities deform, which should provoke a flexoelectric effect.
According to the calculations of the authors, a potential difference of ± 1-10 volts occurs. This is enough to provide electrification by friction.
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The model is in good agreement with several types of experimental results. So, she explains why objects are charged by friction, even if they are made of the same material. The non-uniform distribution of the triboelectric charge also becomes clear. In addition, the theory perfectly predicts the results of measurements of the surface charge density.
We add that this discovery promises practical benefits. Thus, electrification by friction is used in a variety of devices. And in other cases, on the contrary, it must be prevented, because a slipped spark can cause a fire. A deeper understanding of the nature of the effect will allow engineers to use it more effectively or, conversely, get rid of it.
And, of course, it's nice to know why your beloved cat lets out sparks (although it is possible that this is still ancient cat magic).
Anatoly Glyantsev