The Wintertime Static Jump-Start

Among the blessings I count when the snow of winter becomes the mud of spring in interior Alaska is that I will no longer get zapped every time I touch a faucet or a light switch --or kiss my wife.

The tiny but annoying shocks that we administer to ourselves in the winter come from static electricity. It's called static because it isn't moving through a conductor such as a wire--the charge just sits there on the surface of whatever has picked it up. When we shuffle across the floor on cool, dry days, our shoes pick up electrons from the rug. From these, our bodies accumulate a negative charge (an excess of electrons). Then, whenever we touch a grounded object such as a radiator or a less-charged human being, a spark made up of these excess electrons will jump from our fingers to the object.

A good way to discharge yourself without making bodily contact is to carry a coin or a key around, touching anything that looks suspicious with it first. It works and it makes a very satisfying snap and spark, but it makes you feel very silly.

Even though the total amount of current which flows when a spark jumps the gap is insignificant, the voltages involved are awesome. For instance, it requires a "potential difference" of 30,000 volts for a spark to jump a 1 centimeter gap (about 3/8 of an inch) between two-spheres 1 centimeter in diameter--the size of a small fingertip.

Why are we so much less likely to have these shocking experiences now that spring is here? The answer is that the warmer air we now enjoy holds more moisture than does the cold air of winter, and that moisture is what saves us. Air is a poor conductor (in fact, it makes a pretty fair insulator) but it will provide a pathway through which a spark can travel- in a vacuum, a spark can't jump a gap no matter how much voltage is applied. Damp air is a better conductor than dry air, so static electricity need not build up very far before it "leaks" out of the air to surrounding objects. Dry air is such a poor conductor that a charge will build to very high levels before the air's resistance is overcome and a spark jumps to ground.

Beyond the confines of carpeted homes, static electricity can be far worse than a mere nuisance. To take one example, an airplane can accumulate excess electrons from the air by its movement through it, just as your shoes pick them up from the rug. In the early days of aviation, this affected flight instruments and, to make matters worse, the static electricity could discharge on landing. In 1937 a spark from static electricity may have set off the explosion of the hydrogen-filled dirigible Hindenburg when it was docking at Lakehurst, New Jersey. Even today, gasoline trucks usually have a dangling wire or chain to drain off any charge that might spark and ignite their cargo.

Unless static electricity has a place to flow, however, the human body can accumulate a massive charge with no adverse effects. Suitably insulated from the ground, your body could be charged to a potential of millions of volts, and all that you would feel is a slight tingle. However, because all those electrons repel each, other, the ones clinging to your hair will make it frizz out like something the post-punk groupies would love. And if you were to touch the radiator while you're charged like that, you would electrocute yourself.