Why do electrons move from amber to wool during static electricity charging? We know our word for electron comes from the Greek word for amber, since the ancient Greeks experimented with static electricity by rubbing amber on wool.
We know that a static charge is built up by the electrons in the amber moving to the wool.
But why do the electrons move? Aren't they happy orbiting the protons of their own atoms? (Or happily caught in the bonds of their molecules?)
Why would an electron go travelling simply by rubbing? (And stay there?)
My question is: Why do electrons move from amber to wool during static electricity charging?
 A: Electrons, like gas molecules, will diffuse.   So, a material with
a high concentration of surface electrons will lose some to any material
nearby that has a lower concentration.   
The diffusion halts when buildup of
charge creates sufficient voltage drop to reach equilibrium between
ohmic (field-driven) current and diffusion-driven current.
There  may only be a fraction of a volt in such a contact potential, but 
the very short distance between objects in contact means high
capacitance.   Capacitance equals charge divided by voltage, so the charge 
can be significant.
Of course, when you pull nonconducting objects
apart, the gap between the net-positive and net-negatively-charged objects
is increased, and separation does work on the charges,  i.e. it raises the voltage.
If those objects
are conductive, pulling them apart doesn't create much electric separation,
because the charges can conduct to the last few square microns of contact area,
and the resulting smaller capacitance effectively neutralizes the objects even
with the same small contact voltage present.
