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Static electricity refers to the built up electric charge on the surface of objects. The static charges remain on an object until they are bled of to a ground or are discharged. Charge exchange can happen when any two surfaces come into contact, but a static charge only remains when at least one of the surfaces has a high resistance to electrical flow(electrical insulator). Most people have felt the effects of static electricity when they touch a charged surface like a car door or rub their feet on carpet and touch someone else. That little snap of electricity makes for a pretty fun game.
The materials we observe are all formed from molecules that are electrically neutral(equal protons and electrons). Static electricity requires a disparity of positive and negative charges. When two materials are in contact, electrons may move from one material to the other, which leaves an excess of positive charge on one material, and a negative charge on the other. When the materials are separated they retain this charge imbalance.
Electrons can be exchanged between materials on contact; materials with weakly bound electrons tend to lose them, while materials with sparsely filled outer shells tend to gain them. This is known as the triboelectric effect. This effect causes one material to become positively charged and the other negatively charged. This is the main cause of static electricity in everyday life from rubbing different materials together. The release of a charge from this effect is called contact-induced charge separation. Contact-induced charge separation causes your hair to stand up and causes static cling in your clothes.
When a charged object is brought close to an electrically neutral object a separation of charge within the conductor occurs. When this happens charges of the same polarity are repelled and charges of the opposite polarity are attracted. The force due to the interaction of electric charges falls off rapidly with increasing distance, so the effect of the closer(opposite polarity) charges is greater and the two objects feel a force of attraction. The effect is greatest when the neutral object is an electrical conductor because the charges are more free to move. This is called charge-induced charge separation. Grounding of part of an object with a charge-induced charge separation can permanently add or remove electrons, leaving the object with a permanent charge. This is concept is integral in generators used to demonstrate static electricity.
Static electricity is all around you. The next time you reach for something and get a little jolt you will understand the underlying causes.
We’ve also recorded an entire episode of Astronomy Cast all about Electromagnetism. Listen here, Episode 103: Electromagnetism.