2 balloons, piece of the thread
We blow up balloons and hang them up on threads close to each other but without direct contact.
Next we rub them energetically with piece of fabric or dry paper.
On the basis of this experiment it is possible to state that rubbing some substances is triggering changes causing interaction. It is possible to divide electrifying materials in two categories.
Materials belonging to the same category after charging are pushing off, and materials belonging to all sorts categories attract each other.