This experiment is one that I played with while waiting for the time for my Electricity show to start. I started with one balloon, and then added another. Then I began experimenting with other materials, and managed to pass the time very quickly.
To try it yourself, you will need:
- two or more balloons (small, cheap ones work best)
- a flat surface
First, blow up the balloons and tie them off. Rub one balloon briskly against your hair, and see if it will stick to your hair when you release it. If it does not, then use a hair drier to dry the balloon and your hair, and try again. Once the balloon does stick, you are ready to try the experiment.
Rub both balloons against your hair. You want to get a strong static charge on both. Once they are charged, place one of the balloons on a flat surface. Then bring the other charged balloon near it. The balloon in your hand should push the other balloon away. If they are both well charged, you should be able to chase the free balloon around, pushing it with the static charge from the balloon in your hand.
Why does it work? Static charges are much like magnetic charges. Opposite charges attract, and like charges repel. With magnets, the north pole of one will stick to the south pole of another. That is what happened when you stick the balloon to your hair. As you rubbed the balloon against your hair, the balloon picked up electrons and got a negative charge. Your hair lost electrons, leaving it with a positive charge. Positive and negative attract, just like the north and south poles of the magnets.
Since you rubbed both balloons against your hair, both balloons have a negative charge. Two negative charges will repel, pushing away from each other, just as two like magnetic poles do. As you bring the charged balloon in your hand near the charged balloon that is free, the like charges repel, pushing the free balloon away.
You might try using three balloons, holding a charged balloon in each hand to chase the free balloon. What happens if you trap it between the two balloons in your hand? What happens if you toss all three into a small box? I found that the last one would often jump back out, being repelled by the balloons already inside the box. This is especially fun when doing static experiments with balloons in a classroom. After all of the students have been rubbing the balloons on their hair, chairs, etc., have them put all of the balloons into a box for storage. If the air in your classroom is nice and dry, they should find it a challenge, as the balloons will keep pushing each other out of the box.