Objective

The objective of this experiment is to demonstrate the repelling force between two objects of the same charge.

Materials Required

2 equally sized balloons (the experiment can also be performed using plastic stick pens)
2 feet of string
a wool cloth (other fabrics will also work)

How To Build It

Blow up the balloons to equal size. Now tie a piece of the string to the end of each balloon.

Experiment

Hold the string at its center and allow the balloons to hang down. The balloons simply bounce into each other. Now rub the wool cloth across both of the balloons where they made contact with each other. Let the balloons go again. Notice how this time they do not touch. They now repel each other.

Troubleshooting

If the balloons do not repel each other after you have rubbed the wool across them, try the following:

1. Make sure the balloons do not touch while you are rubbing the cloth against them.
2. Make sure the balloons are approximately the same size.
3. Make sure to rub the balloons with wool in one direction only.

1. Why did the balloons repel each other?
   ANSWER: Rubbing the wool cloth across the balloons gave both of them a negative charge, and like charges repel each other.

   Why do your hairs stand out when you walk across a woolen carpet?

   ANSWER: Walking across the carpet gives you an electric charge. Every one of your hairs becomes equally charged, and thus they try to repel each other. This causes the hairs to stand straight out.

Experiments with Everyday Objects by Kevin Goldstein-Jackson. Prentice-Hall, Inc. 1978. p. 156.

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