University of Virginia
Physics Department

Static Electricity with Salt & Pepper

A Physical Science Activity

2003 Virginia SOLs

 

Objectives

Students will

 

Motivation for Learning

Demonstration

Materials

 

Procedure

  1. Ask the students if they think you can pick-up the tissue paper with the ruler.
  2. Try to pick up the pieces of paper with a ruler that has not been charged.
  3. Next, ask the students if they can think of what you could do to the ruler to enable it to pick up the pieces of paper.
  4. Use the materials listed above to try to demonstrate to the students what materials will charge the ruler and which ones won't.
 

Background Information

 Click here for background information on static electricity.

 

Student Activity

To print out the Student Copy only, click here.

Materials

 

Procedure

Using a Sheet of Paper

Using a Petri Dish
  1. Have the students measure out one teaspoon full of salt and one teaspoon full of pepper onto the sheet of paper.
  2. Use a pencil's eraser top or pen top to mix the salt and pepper together.
  3. Have the students take the plastic ruler/rod and rub it with the wool/fake fur.
  4. Approach the pepper with the ruler/rod from above slowly. The pepper will begin to jump onto the ruler. As you get closer to the mixture, the salt will eventually begin to jump to the ruler. The pepper will jump to the ruler/rod and stick.
  1. Have the students measure out one teaspoon full of salt and one teaspoon full of pepper into the petri dish.
  2. Place the cover on the petri dish and mix well by gently swirling.
  3. Have the students rub the top of the petri dish with the fur. Turn the petri dish over for a few seconds and then turn it back to the original position. The pepper should stick to the top of the petri dish.

 

 Data Sheet

To print out the Data Sheet only, click here.

1. What made the pepper stick to the cover of the petri dish or to your ruler?

 

2. What did the rubbing do to the petri dish cover or to the ruler?

 

3. Why does pepper "jump" to the ruler before the salt?

 

4. Can you think of other ways to separate this mixture?

 

5. If you do the extensionů Why did the pepper only stick to the rubbed areas of the petri dish lid?

 

Answers to Data Sheet

  1. The uncharged pepper particles were attracted to the petri dish or ruler as opposite charges were induced in the pepper. Since pepper is lighter than salt, it takes less effort for pepper to overcome the force of gravity.
  2. Rubbing the plastic surface with the fur/wool caused the plastic surface to become charged with static electricity. (There was an excess of electrons left on the plastic from the fur/wool).
  3. Since pepper is lighter than salt, it takes less effort for pepper to overcome the force of gravity.
  4. You can place both the salt and pepper into water. The pepper will float and the salt will sink. You can skim the top of the water and remove the pepper.
  5. Using the stencil allowed rubbing the petri dish lid at certain confined areas. Only those areas that were touched with the fur/wool were charged.

 

Extensions

If using a petri dish, you can expand on this lab. Let the students dump out their mixture and clean the petri dish. Start with a clean, dry petri dish. Next, let them add a pinch of pepper to the petri dish. Place the lid back on. The students can now take a piece of paper and cut it the same size as the lid to the petri dish. Once this is done, have them cut out a stencil from this paper. Next, have the students hold the stencil on the lid and rub the open area (the cut-out area) with the fur. Remove the stencil and turn the petri dish over for a few seconds and turn it back over again to the original position. They should see their stencil of pepper sticking to the cover.

 

Students with Special Needs

Adapt as needed to children who have physical disabilities. For children with physical disabilities, I would put the salt and pepper in a petri dish for them if you are letting the other children do this. I would ask your resource teacher for additional help if you need it.

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

  

Assessment

Data sheet to be completed during the laboratory.