The build-up of charge on insulating materials that can cause sparks when discharged
All materials contain positive protons and negative electrons
Normally, the positive and negative charges cancel each other out, making most materials neutral overall
Rubbing materials together
Friction causes electrons to be rubbed off one material and onto the other
Conducting materials
Materials where electrons are able to move, so the transferred electrons flow back and no charge builds up
Insulating materials
Materials where electrons can't flow back, so the transferred electrons leave a positive static charge on the material that lost them and a negative static charge on the material that gained them
The way electrons get transferred
Depends on the specific materials involved
It's only the negative electrons that are transferred, the positive static charges occur because an object has lost negative charge and not because it's gained positive protons
Charge build-up on an object
1. As more electrons are transferred, a potential difference develops between the charged material and the earth or any earth object
2. If the potential difference is large enough, electrons can jump across the gap, causing a spark
Charges can sometimes build up on conductors too, it's just much less common
Touching a charged car can result in an electric shock, which is a small spark from the car discharging to the earth through your body
