HOW COME?: Understanding static electricity

On a winter's day it's not enough that we hesitate before reaching out to touch a doorknob. Now we have to fear the faucet?

The zaps and sparks that fly in dry rooms as we scuff carpets and rustle clothes are just proof that opposites attract. In this case, the opposites aren't Valentine sweethearts, but electrical charges.

It all comes down to the atoms that make up everything, from combs to doorknobs to our hands. Each tiny atom is normally electrically neutral. Positively charged protons at the center are balanced by an equal number of negatively charged electrons, moving in a kind of cloud around the nucleus.

Losing an electron or two will suddenly make an atom positively charged; gaining one or more electrons will mean a negative charge. A positively charged atom is an electron magnet. Likewise, an atom with too many electrons is primed to unload its extra electron passengers.

And that explains what happens when you shuffle across a carpet and get zapped by a doorknob. Your body picks up extra electrons, giving you a slight negative charge. Touch a metal doorknob (a good conductor), and you'll get a tiny sparking shock as excess electrons flee your fingertips in a mini-current.

Even when so-called static electricity doesn't hurt, it's still annoying. Pull off a knit hat on a frigid winter day, and hair and hat rubbing together dislodges electrons, charging both. The result: Hair follows hat, clinging dramatically, a few crackles thrown in as mini-sparks fly.

Static electricity is worse in winter because both indoor and outdoor air are extra-dry. Humid air helps carry extra electrons off you more quickly; you don't build up much of a charge - so you don't get static shocks.

But if you comb your dry hair with a plastic comb in a dry room, electrons jump from atoms in your hair to atoms on the surface of the comb. Voilà: a negatively charged comb, with electron-poor, positively charged hair clinging to its teeth. (And since "like charges" repel each other, your positively charged strands will have separated in midair, producing that fright-wig look.)

If dryness increases static electricity, how can we get a shock from running water? The water isn't charged; it's electrically neutral. However, positive charges in the water molecules are attracted to stray negative charges on your fingers (which you picked up from the carpet). So as you move your fingers toward the water, its positive charges move toward you. When the charges connect, you get a doorknob-style shock.

You can see the attraction in action shock-free by using a plastic comb. Turn on the faucet to a thin trickle. Then run the comb (say, 10 times) through your dry hair. Bring the now-charged comb to within an inch of the flowing water. The stream should actually bend sideways, attracted to the comb.