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
Things don’t actually touch, their electrons repel each other, and that is what we experience as objects not being able to pass through each other.
When we rub things together, there are a lot of electron interactions happening all at once. Some of those electrons get ripped off of one and stuck on the other object. That’s leaves the donor object with a positive charge and the recipient is left with a negative charge.
The exact properties of the material determine how willing it is to give up or receive electrons. Metal holds onto electrons so loosely that it will balance its charge with whatever it touches. Teflon holds on to its electrons so tightly that it never wants to give up any and it doesn’t have room for any more, that’s what gives it its “non stick” properties.
Stop trying to make grok a thing. I thought we gave up on that back when we all graduated college together – in the late 90s. Remember?
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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