# Why does my car door give me electric shocks?

It’s happened to us all before. You touch your car, door knob or even your cat and –ouch! – receive a small electric shock. They may seem to come from nowhere, but these unsettling (though harmless) shocks are all caused by sneaky static electricity.

### What’s static electricity?

Static electricity is produced when two materials rub against each other, causing a build up of electrical charges.

All materials are made up of negatively- and positively-charged particles. These usually exist in equal amounts, balancing each other out.

But when two materials come into contact, one may ‘steal’ negatively-charged electrons from the other. The result? One material ends up with more negative charges than positive ones, meaning that it becomes negatively-charged overall, whilst the other becomes positively-charged. If the charges cannot move away as they are produced, they accumulate in the material as static charge, or electricity.

You can easily build up a static charge when different layers of clothing rub against each other, when your shoes make contact with carpet as you walk, or when you pull a jumper over your head.

### How does this cause an electric shock?

Once you have built up a big enough static charge, an electric shock is almost inevitable. The moment you touch a conducting material such as metal, the excess electrons jump between your hand and the conductor, giving you a shock.

Let’s take a closer look at what happens while you are in a car. As you enjoy the ride, electrons are exchanged between your clothes and the car seat, building up collections of excess charges. By the time you get out of the car, you have accumulated an overall charge, whilst the vehicle carries the opposite charge. To make things worse, the rubber car tyres and the soles of your shoes are insulators, stopping the charges from escaping to the ground. As you reach to close the metal door, electrons leap between your finger and the car… zap!

### How does the weather affect static electricity?

You may have noticed that you tend to get more static shocks when the air is particularly dry. On damper days, water molecules in the air allow excess electrons to dissipate slowly into the atmosphere, preventing a hefty build up of static charge. Dry air, on the other hand, means that charges have nowhere to go, encouraging the accumulation of static charges and increasing your chances of getting a shock.

Find related sites about static electricity with physics.org

Have a go at making your own static electricity:

http://www.exploratorium.edu/science_explorer/sparker.html

http://www.physicscentral.com/experiment/physicsathome/sink.cfm