Where the charge comes from
Rubbing does not create charge out of nothing. It moves something that was already there — and to see what, you need the inside of an atom.
The three particles, from chapter 3
You met all of this in chapter 3. Every substance is made of atoms, and every atom is built from three kinds of particle.
| Particle | Charge | Where it sits |
|---|---|---|
| Proton | Positive | In the nucleus, at the centre of the atom |
| Neutron | None — it is neutral | In the nucleus, at the centre of the atom |
| Electron | Negative | Moving around the nucleus |
Figure to be added
Only one of the three can leave
Of the three, only electrons can leave an atom easily. So when a cloth is rubbed over a surface, electrons are the only thing that moves between the two — and which way they move decides what charge the surface is left with.
Electrons leave the surface
The atoms on the surface have lost electrons, so the surface is left with more positive than negative. It becomes positively (+) charged.
Electrons arrive at the surface
The surface has taken electrons from the atoms of the cloth, so it now has more negative than positive. It becomes negatively (−) charged.
The charge is on the surface, not throughout
Rubbing affects the atoms on the surface of the object. The charges stay there rather than spreading through the whole thing — which is why the next page has to give them somewhere to go before they will move at all.
Nothing is created, only shared out
If one surface ends up positive, the other ends up negative by exactly as much. Rubbing moves electrons from one object to the other; it never makes new charge.