Brushes are used everywhere for transmitting electrical current between two parts that have an unlimited relative motion.

Brushes are typically made of graphite mixed with some binder. The graphite conducts the electrical current, but it also acts as a lubricant.

The metallic part that is in contact with the brush is called a slip ring, if it is continuous, like in synchronous motors, or a collector ring if it is segmented, like in DC motors or single-phase motors with brushes.