Static electricity

• Static electricity is the build-up of charge on insulating materials and can cause sparks when it's discharged.
• All materials contain charge because they contain positive protons and negative electrons, normally these charges cancel each other out, making most materials neutral.
• If materials are rubbed together, like a bag and a hat, the friction between the two objects causes electrons to be rubbed off one of them and onto the other one.
• In conducting materials like metal, where the electrons are able to move, the electrons just flow straight back again, so no charge ever builds up in insulating materials.
• In insulating materials like a polythene rod and a cloth, the electrons can't flow back, so the transfer caused by the friction leaves a positive static charge on the material that lost the electrons, and a negative static charge on the one that gained them.
• The way the electrons get transferred each time depends on the specific materials involved.
• If a similar cloth is used to rub an acetate rod, the electrons would get rubbed off the acetate rod leaving it positive and onto the cloth making it negative.
• Charges can sometimes build up on conductors too, it's just much less common.
• Cars can build up charge because their metal frame is in contact with the wind which can transfer electrons.
• You've probably experienced this yourself when you've touched a car and got an electric shock, this is just a small spark from the car discharging to the earth through your body.