How come when you rub a balloon on your head your hair stands on end? asks Daniela Prisco.
Have you avoided wearing a hat on a sub-zero day, afraid of the bad-hair aftermath? After scuffing across the carpet in your slippers, have you approached doorknobs warily? Do you pull masses of stuck-together socks out of the dryer? Does rustling your blanket at night produce tiny, crackling sparks?
The culprit, of course, is static electricity, the same phenomenon behind brilliant flashes of lightning in July. Static electricity is a build-up of negative or positive charges.
Most atoms in a material are electrically balanced, or neutral. The positively charged protons at the center (nucleus) are balanced by an equal number of negatively charged electrons whizzing around them. Losing one or more of its negative electrons will make an atom positively charged. Gaining an extra electron or two will make an atom negatively charged.
When you rub a balloon against your head, electrons transfer from atoms in your hair to atoms on the surface of the balloon. Since electrons have a negative charge, the extra electrons have built up a negative charge on the balloon. Meanwhile, in losing electrons, your hair has built up a positive charge.
Since electrical opposites attract, your hair clings to the balloon as you move it away from your head. But since like charges repel each other, your positively-charged strands separate from one another, producing that Bride-of-Frankenstein look.
Sparks sometimes fly when atoms rebalance themselves. When you rub your shoes on the carpet and then touch a metal doorknob, electrons make a tiny leap, with a spark and a zap.
In a list of materials that easily lose electrons, human skin and hair are near the top. So are glass, nylon, and wool. Materials that easily gain electrons include PVC plastic, silicon, and Teflon. While everyday static electricity is annoying, it’s also useful. Electrical attraction is what makes plastic wrap cling. And inside a Xerox machine, the attraction between a charged plastic drum and toner powder helps produce printed copies.
On the down side, static electricity can be dangerous at the gas pump. Gasoline vapors can ignite from sparks produced by sliding in and out of your car seat while the gas is pumping. Can’t avoid re-entering your car? Gas producers recommend touching metal on your vehicle, away from the pump, with your bare hand, to discharge the electron build-up.
Static electricity can even be hazardous on the Moon, where there aren’t any gas pumps in sight. For a few days each month, the Moon sweeps through the Earth’s magnetic field. During the pass, energetic electrons caught in the field strike the lunar surface, charging the moon dust. Much like static-y hair, charged moon dust can actually levitate. Scientists say that when astronauts next visit the Moon, projected to occur in 2020, dust could clog equipment, and sparks could damage delicate electronics.
For more on static electricity, visit www.sciencemadesimple.com/static.html. Rub a balloon on your head and make a soda can race across the room? See how at www.exploratorium.edu/science_explorer/roller.html.