Grade 6, Electricity:
Attraction & Repulsion
Materials: four identical balloons
A wool sweater (silk, flannel, cotton: optional)
A water sprayer
Blow four balloons up to the same size and tie a tread to each of them.
Activate prior knowledge by rubbing a balloon in your hair. Students should be asked to recall their understanding of attraction and static electricity.
Target response: Your hair sticks to the balloon as the balloon is being taken off your hair. This is due to opposite charges "attracting." Extension from previous lesson where they learnt that hair sticks to balloon because each is oppositely charged.
Hold two uncharged balloons together and ask students to predict what will happen. Let the balloons hang without rubbing them. Let the students predict what you will do next and have them predict what might happen.
Target response: Depending upon what the students already know I would expect them to say that the balloons would not attract or repel each other before or after being rubbed.
Now let a student hold the threads, then you rub the balloons with the wool sweater. Let the balloons hang back down, ensuring that the strings are not entwined together. (Balloons will not touch each other). Students should consider if their predictions were correct.
Ask students what will happen if you add another balloon. Add another balloon, which isn’t charged. Have them note the observation. Charge that balloon also with the sweater.
If the wool has the same charge each time I rub the balloons and the balloons have the same charge after rubbing them, why did what you observed, happen?
Target response: Since we know that opposite charges attract, such as the case with the hair and balloon, like charges will repel. That is why the balloons did not touch each other
Students should consider how to make them come together again. Mist the balloons with water and demonstrate how they come together once again.
Students should conceder where they have encountered this type of phenomena in their world.
Target response: From what I previously taught them I would hope that the students would give a few examples of static electricity and then tell me that it would be best to do experiments outside during the winter. In the winter there is less moisture in the air thus water cannot serve as a means to neutralize charges of the objects thus the objects can have an overall charge. In essence, the water serves as a carrier of charges, also known as an electrolyte.
Use other fabrics to check for alternate results.
Spray only in the vicinity not directly onto the balloons.
Relate to current electricity and the use of insulators and how water is a conductor. Ask if electricity could jump (arch) from a power line and electrocute a passer by.
Why did the balloons repel each other after they were rubbed together?
Would there be a difference if we used another fabric? E.g. silk, cotton, leather, flannel, fleece. Explain your answer.
Why did they fall back together after spraying water?
Would it have made a difference if it were a different liquid? Explain why.
How else could we have gotten them to fall back together?
Does the experiment confront the prior conceptions the students had?
What needs to be done to get the balloons to fall back together?
If I had spayed only in the vicinity rather than directly on the balloons would it have effected their repulsion? Why?
Would classroom conditions vary our results? Why?
During which time of year would it be best to experiments on static electricity? Explain your answer.
Where do you see examples of static electricity in our environment?
What is damp weather doing to the electric charges?
What is meant by opposites attract?
Where have you seen this in real world conditions?
What does neutral mean?
Can water carry an electric charge? Where have you seen evidence of this?
Is this seen in the experiment?
What kind of charge does your clothing have versus the balloon when a balloon is attracted to your clothing?
After rubbing the balloons, they were charged with the same charge and thus they repelled each other. By spraying water droplets in their vicinity, the water droplets carry the charges away from the balloons, rendering them neutral, as a result the balloons fall back together.
Another way to neutralize the charges on the balloons is to touch them with a damp cloth or a moist hand.
Liem, Tik L. (1987). The Balloon Electroscope. Invitations to Science Inquiry, p244.