Electrostatic Force: Making Salt and Pepper Dance

Grade Levels: 3 - 5

Objectives

  • Students will observe, infer, predict, experiment, formulate hypotheses, and identify and control variables.

Materials

  • Balloon
  • Wool cloth
  • Salt and pepper

Procedures

  1. Inflate the balloon and tie the end.
  2. Sprinkle a small amount of salt and pepper on a sheet of paper or on your desk top.
  3. Rub the balloon with the cloth.
  4. Bring the balloon within about an inch or two (2-5 cm) of the salt and pepper.
  5. Observe for a minute or two. You will need to caution your students to watch very carefully. Otherwise they will probably not notice that the same grains of salt and pepper are attracted to the balloon, repelled, then attracted again over and over.
  6. Explain what is happening and why:
    In this activity you will see the salt and pepper do a "dance" because of the following principles. The balloon, being rubbed with wool, takes on a negative charge. When it is held near the salt and pepper, the salt and pepper become charged positively by induction and will leap and cling to the balloon. As the salt and pepper remain in contact with the balloon, some of the negative charge (electrons) will drain off the balloon and onto the salt and pepper. The salt and pepper now have a negative charge – the same as the balloon – and will leap from the balloon. Notice that the salt and pepper do not simply fall, but rather they appear to be thrown from the balloon by some force. The force is the repelling action of the electrostatic charges for each other.

Excerpted from Hands-On Science Activities for Grades 3-4.

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