Static electricity: why door handles give you a shock

In short: When two materials rub against each other, electrons can pass from one to the other. The objects are then electrically charged, and at the next contact the charge often evens out with a small spark.

In more detail: Normally an object contains equal amounts of positive and negative charge. Rubbing, or even just touching and separating, shifts this balance: one object then has too many electrons, the other too few. Like charges repel each other, opposite charges attract.

In detail

• The shock at the door handle: Walking across a carpet charges up your body. When you then touch metal, the charge flows away suddenly and you feel a brief sting.
• Dry air: In winter, heated indoor air is often dry. Humid air drains charges away more easily, so sparks are more frequent when the air is dry.
• High voltage, little energy: The voltage can reach several thousand volts, but the amount of charge is so small that the shock is harmless for healthy people.
• Hair and balloons: If you rub a balloon on your hair, it sticks to the wall, and your hair stands on end because the similarly charged hairs repel each other.
• Clothing: Synthetic fabrics become charged particularly easily. Fabric softener and clothes made of natural fibres can reduce the crackling.
• Electronics: A discharge can damage sensitive components. When working inside a computer, you therefore touch an earthed metal part first or wear an anti-static wrist strap.
• Danger when refuelling: In rare cases a spark can ignite petrol vapour. That is why, at filling stations, you should briefly touch metal on the car after getting in or out before taking hold of the nozzle.
• Useful applications: Laser printers and photocopiers, dust filters in power stations and the powder coating of metal all make use of electrostatic attraction.
• On a large scale: Lightning is a huge electrostatic discharge between clouds and the ground (donner-und-blitz, strom).