Final answer:
When certain materials are rubbed together, charges can be separated, resulting in one material becoming positively charged and the other becoming negatively charged. This occurs due to differences in the affinity for electrons between the materials.
Step-by-step explanation:
When certain materials are rubbed together, charges can be separated, resulting in one material becoming positively charged and the other becoming negatively charged. This happens because tiny amounts of charge are transferred from one material to another.
For example, when glass is rubbed with silk, negative charge is transferred from the glass onto the silk, making the glass positively charged and the silk negatively charged. This occurs due to differences in the affinity for electrons between the materials.