Static electricity — Physics, 7–10
Electric charge can build up on an object and then attract, repel or suddenly jump away. Rubbing and separating materials often makes this easier to notice.
Charge that stays for a while
Some materials can gain or lose tiny electric charges when they rub against other materials. The charge may stay on the surface instead of flowing around a circuit, so it is called static electricity. Charged objects can pull on light things, and charges of the same kind can push apart.
Why people noticed it
Long before electric circuits were understood, people saw rubbed materials behave strangely: amber could attract small bits of straw. This was a problem because the effect was mysterious and sometimes caused sparks. Studying static electricity helped people recognise that invisible electric charge can move between materials and discharge suddenly.
A balloon and hair
Rub a balloon on dry hair about 20 times. Electrons move between the hair and the balloon, leaving them with different charges. Bring the balloon near the hair: the hair is attracted and may stand up. Touch the balloon to a metal tap and you may see or feel a tiny spark as charge spreads away.
The static-electricity mistake
A common mistake is thinking that only one material becomes charged when two materials are rubbed. Rubbing helps electrons move from one material to the other, so both are affected, usually with opposite charges. It is also reasonable to expect a spark every time, but dry air and enough charge are needed.
Where it appears
Static electricity can make clothes cling after drying and dust stick to screens. Lightning is a huge natural discharge between charged regions in clouds or between a cloud and the ground. Factories also control static charge when making electronics, because an unexpected spark can damage tiny parts.
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