You and Your Students!
Vicki Cobb, Education World Science Editor
Play with static electricity.
Physical Science, Electricity
Setting the Scene (Background)
You can’t feel a magnetic field, but you can sense an electrical one. In these activities you and your students will generate static electricity. The word “static” means “standing still.” Once an object has a static electrical charge, the electricity doesn’t go any place unless you touch it to an object that can “ground” the charge. These activities will -- literally -- make your students’ hair stand on end!
It is easier to generate static electricity on a dry day. Moisture in the air causes static electricity to “leak” away. This activity leaves lots of room for discovery, so it’s a good one for students to do with a partner.
Provide each pair of students with a blown-up balloon. Have one student rub the balloon on a sweater or a wool scarf. The balloon is now "charged." Move the balloon over a bare arm without touching it to the arm. Feel the hair stand on end?
Next, move the charged balloon near someone's hair. See how the hair is attracted to the balloon.
Now touch the balloon to an arm. What happens to the electric field? (It disappears.) The electricity "ran" into the arm. You can recharge the balloon by rubbing it against wool again.
A balloon that has an electric field can do some strange things. Stick a charged balloon on a wall. It stays where you put it!
Move a charged balloon over some dried cereal, such as a puffed-rice cereal. If it gets too close, some of the cereal will leap up and attach itself to the balloon. The cereal actually dances!
As in the previous activity, you can make the field disappear by touching the charged area with your hand, to some other object, or to the ground. When you give a charge a way to disappear, you are "grounding" it.
On a rainy day, the charge "leaks" away to moisture in the air. But if the day is crisp and dry, you may have a hard time grounding your balloon. Rub it with a fabric-softener sheet. The anti-static ingredients in the sheet do the job!
Pull off a piece of Scotch Magic Tape about 6 inches long. Bring the tape close to a charged balloon. Does the tape move toward the balloon or away from it? (It is attracted to the balloon. You will see the "electric wind" caused by the charged balloon.) Stick the tape to a Formica countertop leaving an end free. Quickly pull the tape off the countertop to charge it. Then bring the tape near the balloon. What happens? (The tape is repelled.)
Behind the Scenes
There are two kinds of static-electric charges: positive and negative.
You may recall that an atom is made up of particles with electric charges. The nucleus of the atom is positively charged; orbiting electrons are negatively charged. An uncharged atom is electrically neutral -- that is, the magnitude of the negative charge is equal to the magnitude of the positive charge.
When you rub a balloon with wool, it gains electrons from the wool. That gives the balloon a net negative charge (while the wool becomes more positive).
When you bring the charged balloon near another object (such as hair) -- without letting it touch that other object -- the opposite charge can appear in the hair. (This is called an "induced" charge.) As a result, the positively charged hair is now attracted to the negatively charged balloon.
The rule for the static electric field is that opposite charges attract, like charges repel. When you ground a charged object, the electron balance is restored and the object again becomes electrically neutral.
For more information and activities for teaching about fields of force, check out
Sources of Forces: Science Fun with Force Fields
by Vicki Cobb, illustrated by Steve Haefele (The Millbrook Press, 2002).
Article By Vicki Cobb
Copyright © 2004 Education World