Contact electricity generated by friction

In this experiment, the students generate frictional electricity by using different materials and demonstrate this with the electroscope. They learn that

• electrically neutral bodies have compensating positive and negative charges.
• when two different materials come into intensive contact, such as through rubbing, then the electrical neutrality of these bodies can be disturbed: They become charged with opposite polarity.

The polarity of the charge is not typical for a specific substance, but rather depends on the interaction of the two materials that are rubbed against each other.