Observe the electromagnetic force by investigating when electrically charged objects attract and repel one another.
To observe the electromagnetic force. Specifically to observe when electrically charged objects attract one another and when they repel one another.
The electromagnetic force is one of the four fundamental forces in nature. When you rub certain materials together, electrons can be transferred from one object to another, creating electrical charges.
Static electricity is a buildup of electrical charges within or on the surface of a material. When you rub a balloon in your hair, the balloon picks up electrons and becomes negatively charged, while your hair loses electrons and becomes positively charged.
A Van de Graaff generator is a device that creates static electricity at a much higher voltage than simple friction methods. It uses a moving belt to accumulate electric charge on a hollow metal sphere. The generator can create charges strong enough to produce visible sparks and can cause hair to stand on end when a person touches it. It's an excellent tool for demonstrating the principles of electrostatics and the movement of electrical charges.
Blow up the balloons and tie them off so they each stay inflated.
Tie some thread to one of the balloons and attach the other end of the thread to the ceiling or the center of a door frame with some tape so that the balloon hangs from the thread. Make the length of the thread so that balloon one hangs at about the same height as your chest.
Take the balloon that is hanging by the thread and rub it in your hair a little. This will cause the balloon to pick up some electrical charge. Now back away from the balloon and allow it to hang there.
Take the other balloon and rub it in your hair just a little. Hold this second balloon in both your hands and slowly bring it close to the balloon that is hanging from the thread. What happens?
Play with the situation a bit, trying to see what kind of motion you can induce in the hanging balloon. Record your observations in the data table.
Vigorously rub the balloon that is in your hands in your hair. Spend significantly more time doing it this time compared to what you did in step 4.
Once again, bring the balloon in your hands close to the balloon that is hanging on the thread. Note what happens and note how the motion of the hanging balloon compares to the motion in steps 5 and 6.
Put away the balloon that is in your hands.
Take a piece of tape that is at least 15 cm long and tape it to the top of a table. Leave a little part of it unstuck, so that you can remove it in a moment. Be sure to ask your parents which table you should use for this, as what you will do in the next step can damage the finish on some tables.
Quickly rip the tape off the table and grasp it at both ends. Hold the tape near the hanging balloon, with the sticky side facing the balloon. What happens this time?
Once again, play with the situation a bit to see what kind of motion you can induce in the hanging balloon. Record your observations.
If you have access to a Van de Graaff generator, set it up on a non-conductive surface. Make sure it is unplugged before setup. Have an adult supervise this part of the experiment.
Before turning on the generator, ensure everyone is wearing eye protection. Keep all electronic devices at least 3 feet away from the generator. People with pacemakers or other electronic medical devices should maintain a safe distance.
Have an adult turn on the Van de Graaff generator. Allow it to run for about 30 seconds to build up a charge on the metal dome.
Place small pieces of aluminum foil or paper clips near (but not touching) the dome of the generator. Observe what happens. Try different distances and record your observations.
Bring the hanging balloon (from earlier steps) near the Van de Graaff generator dome without letting them touch. Observe the interaction and record what happens.
Rub a plastic rod or ruler with a piece of wool or your hair to charge it. Then bring it near the dome of the generator. Observe and record what happens.
Turn off and unplug the Van de Graaff generator. Clean up and put everything away.
| Step | Action | Observations |
|---|---|---|
| 4-5 | Lightly charged balloon near hanging balloon | |
| 6-7 | Vigorously charged balloon near hanging balloon | |
| 10-11 | Charged tape near hanging balloon | |
| 15 | Small metal objects near Van de Graaff generator | |
| 16 | Hanging balloon near Van de Graaff generator | |
| 17 | Charged plastic rod near Van de Graaff generator |