Summary

Net charge changes only when charge travels in and out of a system.
Charging usually happens through electron transfer.
Induced charge separation polarizes an object without contact. Happens in neutral conductors and insulators.
In conservation problems, charge of separated objects should sum to charge of system.
Grounding occurs when a system connects to a large neutral object.
Conductors let electrons move easily, insulators only let bound charges shift slightly.
Main 3 ways to charge: friction induction contact.