Imaginary Shelf

Objectives

• Describe the movement of electrons from one material to another.

Materials

• Per Student:
  balloon
  a clean blackboard, whiteboard, or dry wall space

Key Questions

• How are the balloons sticking to the board?
• What did rubbing against a sleeve do to the balloon?
• Do the balloons stick to the wall forever? Why or why not?

What To Do

1. Blow up 3 or 4 balloons. Tell students that you have constructed an invisible shelf on the blackboard.
2. Rub the balloons against your sleeve or shirt as if cleaning them, then stick them to the blackboard in a horizontal row. The point is that you do not want to implicitly show them that you are actually rubbing the balloon to charge it.
3. When students catch on about the rubbing of the balloons, have them try to make a second lower “shelf” with the other balloons rubbed against their hair or shirt.

Teacher Tip: Test this demo in the classroom before the class starts. It may or may not work depending on the material of the walls and/or the humidity conditions.

Extensions

• Try rubbing a balloon against different materials such as wool, silk, cotton, plastic, hair.
• Do you find any difference in the static charge built up?
• How about the length of time it sticks to the board?
• In teams of 6–7 students, choreograph an “electron dance”. Show the movement of electrons, the charge of the balloons and the charge of the wall.