When you rub a balloon on your hair, you’re transferring electrons from a mostly neutral source to a mostly neutral recipient. Why do they go at all, and why is it always from one to the other? What makes the balloon want my electrons more than my hair does? It would seem reasonable that after the balloon *does* steal some, it would immediately start returning them when you keep rubbing since your hair is now positively charged.
In: Physics
Maybe the balloon isnt stealing them, maybe the electrons just aren’t that into you?
The [triboelectric effect](https://en.wikipedia.org/wiki/Triboelectric_effect) is the official name of that transfer of electrons.
With different materials brought into contact, electrons will shift from one surface to the other — whichever direction is favored by the total balance of molecular forces & lower energies. When enough electrons have transferred, there’ll be an opposing electrostatic force that’ll limit any further transfer. Different material combinations will therefore “max out” (so to speak) at different levels of transferred charge.
Hair and a rubber balloon is a good combo. Another fun experiment is to rub a length of PVC irrigation pipe with something, on a dry day, and hold it horizontally to levitate a thin plastic shopping bag above it (thin plastic bags still not banned in California, at Home Depot checkout).
Low humidity days will maximize the transferred charge, by reducing the rate of electrons moving back the other way.
Edit: Lemme just write a new explanation:
When you rub a balloon against your hair, the rubber of the balloon takes electrons from your hair. This gives your hair a positive charge (lack of electrons) and the balloon a negative charge (excess electrons). Your hair will be attracted to the surface of the balloon (unlike charges attract). You will also notice that your “hair stands on end” even if the balloon is not near. This is due to the fact that all hairs are positively charged and hairs with the same name repel each other.
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