When does friction generate static electricity?

Friction generates static electricity primarily when two different materials rub against each other, a process known as triboelectric charging. During this interaction, electrons can be transferred from one material to another, leading to an imbalance of electrical charge on the surfaces involved. This charge separation creates static electricity, which can manifest in various forms, such as attracting lightweight objects or producing a spark when the charge is discharged.

In scenarios involving water, it generally acts as a conductor rather than a generator of static electricity. The closing of a circuit pertains to the flow of current rather than the generation of static charge. Heating materials can influence their resistance or conductivity but does not directly relate to the generation of static electricity through friction. Therefore, the interaction of different materials under friction is the key mechanism for generating static electricity.