When you rub two things together (your socks on a carpet, a balloon on your hair) tiny electrons get scraped off one and stuck onto the other. Now one thing has too many electrons and the other has too few, so one is negative and one is positive. That's a charge imbalance, and it wants to even out. It can't, because air doesn't let it leak away easily, so it just sits there building up on you. The moment you touch something that can take it (a metal doorknob, a friend) all that charge leaps across in a single tiny spark. That's the snap and the sting. Go rub the balloon in the simulator, watch the hair stand up, then touch the doorknob and catch the spark.
Most people think the doorknob zaps you. In fact you were holding the charge the whole time, built up step by step across the carpet, and the metal was just the first thing that let it leap away.
What's actually happening
Almost everyone thinks the shock comes from the doorknob — that the metal somehow zapped you. It didn't. You were the one holding the charge the whole time, and the doorknob was just the first thing innocent enough to take it. The charge was assembled, step by quiet step, as the soles of your shoes peeled off a carpet thousands of times, each peel scraping a few electrons across the boundary between two materials.
Here is the real mechanism. When two different surfaces touch and separate, electrons hop from the material that holds them loosely to the one that grips them tightly. Rub a balloon on your hair and the balloon wins the electrons: it goes negative, your hair goes positive. Now every hair carries the same kind of charge, and like charges repel, so the hairs shove each other apart and stand on end. Nothing was created — electrons were simply moved, leaving a deficit on one side and a surplus on the other. The voltage between you and the room can climb to 20,000 or 30,000 volts, which sounds lethal but carries almost no current, so it only stings.
The surprising part is the role of the weather. The charge can only build if the air refuses to carry it away, and dry air is an excellent insulator. Humid air is faintly conductive: a film of water on every surface quietly bleeds the charge off as fast as you make it, so you never accumulate enough to spark. That is why static shocks are a winter phenomenon and why they barely happen on a muggy summer day. Crack the air below about 30 percent humidity and every doorknob becomes a trap.
Static is electrons scraped from one surface to another, trapped by dry air until something conductive lets them spark across.
- 1Rub an inflated balloon briskly on your hair or a wool jumper for a few seconds, then lift it away — your hair follows it, because opposite charges attract.
- 2Hold the balloon flat against a wall and let go. It sticks, because its negative charge pushes electrons in the wall away and is then pulled toward the positive patch it left behind.
- 3Wet your hands or breathe on the wall first and try again — the dampness bleeds the charge off and the balloon falls. Humidity is the off-switch.
Common questions
The charge can only build if the air refuses to carry it away, and dry winter air is an excellent insulator. Humid air holds a film of water that quietly bleeds the charge off as fast as you make it, so you rarely spark.
A carpet shock is often 20,000 to 30,000 volts, far more than a wall socket, but it carries almost no current. The total charge is tiny, so the discharge lasts only microseconds and merely stings.
Yes. The triboelectric series ranks materials by how tightly they hold electrons. Rub glass on silk and the glass goes positive every time; the winner and loser never swap.