University of Virginia
Physics Department

## Introduction to Static Electricity

A Physical Science Activity

2003 Virginia SOLs

• PS.1
• PS.11

Objectives

Students will

• learn the difference between charged and uncharged objects and how they interact;
• learn that like charges repel each other and opposite charges attract each other;
• understand the concept of polarization of charge as a means of attraction;
• explore how positive and negative charges are created.

Motivation for Learning

Demonstration: the kissing balloon

Materials:

• Balloon
• Length of thread (2 m)
• Permanent marking pen
• Wool cloth, piece of silk, or fake fur
• Words to the story
Procedure
(while students are out of the room)
1. Inflate the balloon and draw a face on the balloon using a marker.
2. Hang the balloon from the ceiling with thread so that the face is right side up and the balloon is the height of your head.
3. Rub the nose of the balloon with a wool cloth, but nowhere else on the balloon. If properly charged, the balloon will now turn and face you when you are reasonably near ( 40 cm ). If you walk around the balloon, the face should rotate to follow you. If your head gets closer ( less than 20 cm ), the balloon should be attracted to you and "kiss" your face.
4. You are now ready for your students to return to the classroom. Do not allow them to go near the balloon.

(while students are in the room)
Tell the students this story: "Students, I'd like you to meet a friend of mine. His name is George. George, meet the smartest eighth grade in the state." (At this point you are at least 2 meters away from George).
"There are a couple of things I think you should know about George. First, he's nearsighted; does anyone know what that means? He can't see very well far away. Second, he has an awful crush on me. He likes me so much that he just can't keep his eyes off me- when he can see me that is." (Walk over to George and he will turn to face you)
"You see? He just stares at me, and keeps staring at me as long as I'm close enough for him to see me." (Walk away.) When I walk away, he just looks all over, trying to find me again." (Move closer again) "You'll be able to tell when I'm in his range of vision because he'll look right at me." (Walk around George and his face will follow.) "See, I told you he likes me. Now, if you promise not to tell anyone, I'll let George kiss me - just once, and the cheek." (Lean over, where your cheek is very near George. He will kiss you) "Aw, that's so nice."
"Now, for the next few days, we're going to do a few things that should give you some clues about George. We'll visit him again another day." (You can adapt the story however you feel beneficial; George could be Sue, or a faithful old dog. One of the important things is relating eyesight range to electric field range)
(Adapted from Hands on Physical Activities by Marvin Tolman, Activity 7.1 )

Background Information

Everything around us is normally neutral in charge. Water, wood, walls, desks, people, almost everything. We did something to George to make him charged, so he acted funny. But regular objects like desks, pens and pencils are not normally charged. Show students the model of how like charges repel and opposites attract, and if something is charged, it attracts a neutral one by attracting the opposite charges in that neutral object. This is called polarization (it is discussed in the answers to the questions). Tell the students that today they will see how charged objects interact with all these regular objects and how charged objects act with each other. How does something become charged? The simplest way is to rub the charges off. We will be charging balloons today by rubbing one part of them with wool. Does the whole balloon become charged or only where it is rubbed? It is just where you rub. We will put a dot on the balloon so we remember where it was rubbed. We can rub it with a lot of things to make it charged, for example hair is good at charging objects. But it messes up your hair if you rub things on your head. This is why we use a piece of wool, which is actually sheep's hair.

### Student Activity

To print out the Student Copy only, click here.

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?

1. The balloon will attract the cereal at the place that it has been rubbed. Away from the dot, there will be no attraction of the cereal. This is because the charging of the balloon is local; the charge doesn't spread all over the balloon if it is just rubbed in one place. The balloon is an insulator.
2. The balloon will stick to all types of walls as well. The reason for this is that the neutral object is polarizing. When the charged object gets near the uncharged one, it attracts all of the opposite charges closer to the charged object.

3. The balloon will also attract the water for similar reasons to #2. It works much better when the charged area of the balloon is near the water stream.
4. The attraction occurs when the charged balloon goes near the faucet, the wall or the cereal for the same reasons explained in #2.
5. We picked light materials such as the cereal so that we could see the movement due to the polarization. If the objects were too heavy, there would not be enough electrical attraction to overcome the gravitational force.
6. Yes, by taking advantage of the polarizing effect, charged objects can attract neutral objects by moving the charge around on the neutral objects. The unlike charges are then closer than the like charges, and the result is that the attraction is greater than the repulsion. The electrical force goes as q1q2/r2, where the q are charges and r is the distance between the charges.

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 observation.
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?

1. After rubbing the balloons with the wool, the balloons have the same charge and will repel each other.
2. The side of the balloon that was rubbed has been charged and wants to be as far away as possible from the other charged balloon. Therefore, the sides of the balloons that were not rubbed will tend to be closer together. After you have rubbed the entire balloon, it will be difficult to get rid of the charge. If you were going to do this experiment, it might be best to rub half the balloon first and do that experiment, before rubbing the entire balloon.
3. By spraying water droplets on the balloons, charge is carried away from the balloons, which leaves them neutral. This is a good way to neutralize the balloons. As they become neutral, they will fall back together but will not be attracted to each other. Another way to neutralize the balloons is to touch them with a moist or damp hand. One needs to remember that only where the balloons are wet is where the charges are carried away. The part of the balloon that is not wet will still attract to the other balloon where it is not wet.
4. Damp weather reduces the amount of electrical charge, because just like the mist from the spray bottle, the water droplets carry the charge away from the balloons.
5. It is best to do static electricity experiments in the winter when the humidity is less. (Adapted from Invitations to Science Inquiry, 2nd ed. by Tik L. Liem, Activity 9.10)

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.

Children with specal needs

Adapt as needed to children who have physical disabilities. These children may need help blowing up the balloons, tying the thread to the balloon, and rubbing the balloon with the wool. As always ask your resource teacher for additional help if you need it.

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?

1. The salt and the pepper jump from the paper to the ruler. The pepper is more likely to jump to the ruler quicker.
2. The plastic surfaces have become charged with static electricity from the fur, or wool, or silk and therefore are attracting these uncharged particles.
3. The pepper jumps first because the pepper is lighter than the salt.
4. You can place both the salt and the pepper in water where the salt will sink and dissolve. The pepper will float and therefore can be skimmed off the top.

Children with special needs

Adapt as needed for children who have physical disabilities. For children with physical disabilities, you may need to put the salt and pepper in a petri dish for them. Ask your resource teacher for additional help if you need it.

Click here for further information on laboratories with students with special needs.

Assessment

Questions to be completed during the laboratory.

For a copy of just student questions, click here.