As the weather gets colder, the air tends to get drier. When the air is dry we tend to notice static electricity in the air through static shocks to our body. Static electricity refers to the build-up of electric charge on the surface of objects-essentially, when electrons move from one surface to another through contact. If the surfaces are both insulators (substances that do not readily allow the passage of heat or sound), they'll build up an electrical charge. One object will have a positive charge (because it lost electrons) and one will have a negative charge (because it gained electrons). If one of the charged objects then touches a conductor, like a piece of metal, the charge will neutralize itself, causing a static shock.

So how does this affect you and your clothing? It turns out we have a lot of insulators around us: a wool sweater, the rubber soles of your shoes, the carpet in your room. When you walk across the carpet your body builds up a charge that it can´t get rid of through the insulating soles of your shoes so then, when you touch your metal doorknob you transfer the electron charge and - ouch! - get a shock. And as dry air itself is an insulator this tends to happen most commonly in the dry, winter months.

There is a simple at home experiment you can perform to demonstrate how this happens. You will need:

First, blow up a balloon and tie it off. Small, cheap balloon work the best, but any sort should do the job. Then, tear some tiny bits of paper and place them on a flat surface. The pieces should be smaller than your fingernail. Rub the balloon briskly on your hair or a piece of cloth and then bring it near the pieces of paper. If you generated enough static electricity, then some of the pieces of paper should jump up to the balloon. If the paper did not jump to the balloon, then turn on the hair drier and use it to dry your hair and the balloon. Be careful not to get the balloon hot enough for it to pop. Once the balloon is dry, try it again. This time, the paper should jump very well for you.

Next, take the wet cloth and rub it gently over the surface of the entire surface of balloon. You want the balloon to be damp. Then rub the wet cloth lightly over your hair, to make it damp as well. Try rubbing the balloon on your hair again and bring it near the bits of paper. This time, you will get very little reaction, if any at all. Once again, dry the balloon and your hair with the hair drier and the paper will once again jump up to the balloon.

Why would water cause this? When you rub the balloon against your hair, you are transferring electrons (tiny, negatively charged pieces of atoms) from your hair to the balloon. Because electricity does not flow easily over rubber, the electrons are trapped there, building up a strong, negative static charge. It is this charge that attracts the bits of paper.

Rubbing the damp balloon against your wet hair still moved electrons from your hair to the balloon, but the water formed a conducting pathway. Instead of remaining trapped on the balloon, the electrons flowed across its surface to your skin and then to the ground. You never built up enough of a static charge to attract the paper bits. When you used the hair drier to dry the balloon and your hair, you removed this pathway, and once again the static charge could build up.