University of Virginia
Physics Department

## Static Electricity

A Physical Science Activity

### Student Activity

Student Activity #1 - Can neutral objects attract non-neutral ones?

Materials

• 1 balloon
• Small pieces of paper, pieces of sugarless puffed cereal
• Water faucet
• Wall: concrete, metal, plastic
• Wool cloth or a piece of silk

Procedure

1. Blow up the balloon and tie off the end. Put a mark on one side of the balloon. This dot lets you know which area you rubbed.
2. Rub the balloon with the wool at the dot.
3. Put the non-charged (away from the dot) part of the balloon near the pieces of paper and the cereal. Observe what happens.
4. Put the charged (near the dot) part of the balloon near the pieces of paper and cereal. Observe what happens. If nothing happens in this case, vary the distance between the balloon and cereal.
5. Rub the dot again and try to stick the balloon on different walls on the charged and non-charged parts of the balloon: Concrete, glass, metal, plastic. Observe what happens.
6. Put the un-charged and charged part of the balloon near a small water stream from the faucet. Observe what happens.

Questions

1. What happened when you put the balloon near the cereal and paper? Was it any different for the side of the balloon with the dot?
2. Could you get the balloon to stick on all of the different types of walls? How about the part of the balloon not near the dot?
3. Did the balloon attract the water near the dot? Away from the dot?
4. From these experiments, what can you say about how charged objects affect regular neutral objects like paper, walls, and water?
5. Why did we pick less heavy things like paper and cereal in our test rather than something heavy like a pen or a pencil?
6. After all of your observations, do you know now whether charged objects can attract neutral objects?

Student Activity #2 - The Balloon Electroscope

Materials

1. 2 identical balloons
3. Wool cloth, silk cloth, or piece of fake fur
4. Water sprayer per 2 groups

Procedure

1. Blow-up the balloons, tie the ends in a knot, and tie thread to the ends of each balloon.
2. Tie the balloons together using the thread so the balloons are about 80 cm apart.
3. Have one person hold the uncharged balloons by the thread and move the balloons together. Record observations.
4. Rub each balloon all over with the wool as best as possible. Move one balloon near the other but do not allow them to touch. How do they react with each other? Record observations.
5. While the balloons are repelling each other, have the students gently mist the balloons with water

Questions

1. Why did the balloons repel each other after they were rubbed all over with the wool?
2. What would have happened if we rubbed one side of the balloons instead of all over?
3. Why did the balloons fall back towards each other after they were sprayed with water?
4. What effect does damp weather have on electrical charges?
5. During which time of the year would it be best to do experiments using static electricity?

Extensions

An electroscope is a device that shows charge is present. By touching an object to an electroscope (which initially is neutral), charge may be transferred to the electroscope, which then indicates in some way that charge is present. Let the students work in groups and have the students make a new design on paper or actually build an electroscope. They can use different charged objects to show that their electroscopes work. If they are designing on paper or building one, ask them to write down the purpose of the different parts (bottle, stopper, wire, foil, and charged object). If building an electroscope, let the students try out different things to see what works and what doesn't.

Student Activity #3 - Static Electricity with Salt and Pepper

Materials

• Pepper shaker
• Salt shaker
• Piece of wool, silk, or fake fur
• Clear plastic ruler, or plastic rod
• Piece of paper

Procedure

1. Have the students shake out some salt and pepper on a white sheet of paper (no more than a teaspoon each).
2. Use a pencil's eraser top or pen top to mix the salt and pepper together.
3. Take the plastic ruler/rod and rub it with the wool/fake fur.
4. Approach the salt and pepper very slowly with the ruler from above. Observe what happens

Questions

1. Explain what happens after you rub the ruler.
2. Why does that happen?
3. Why did the pepper jump to the ruler before the salt?
4. Can you think of other ways to separate this mixture?