How does static electricity build up?
When 2 insulating materials are rubbed together (using friction), electrons pass from one to the other. This leaves a positive charge on the other one, because losing electrons adds charge. It also leaves a negative charge on the other object because it has now gained electrons.
Only the electrons can move - the positive charge CANNOT move.
This is because the positive charge is only created by the movement of electrons.
When a charge builds up, it can suddenly move, causing sparks or a shock.
This can be dangerous, or it can be harmless, like when you touch someone and you get a small shock.
Charges - attractions and repelling
Opposite charges ATTRACT.
Identical charges REPEL.
+ and + = repel
- and - = repel
+ and - = attract
- and + = attract