I can grok why rubbing things could free electrons, but what makes them move to one of the things being rubbed to create an imbalance?
In: Physics
The things need to be made from different materials. There is a list of materials called the [_Triboelectric series_](https://upload.wikimedia.org/wikipedia/commons/0/00/Triboelectric-series_EN.svg) sorted by how prone they are to get the electrons from another*. The stronger “wins”, and a larger difference usually means that it also takes less “rubbing” per shock value.
It is by the way not rubbing that really causes the effect. It comes from touching and then being ripped apart. Rubbing just does that a lot at microscopic scales. But you can get it also from ripping things apart.
*: there is more to it, it is not a strict list all of the time. But that image should be enough for ELI5.
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