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Imaginary Shelf

Can you stick a balloon to the wall without glue or tape?

This demonstration introduces students to the concept of static electricity and explores the science behind a common party "trick".

When you rub a balloon against your sleeve, your sleeve loses some electrons. The balloon ends up with extra electrons, making it negatively charged. When the negatively charged balloon approaches a wall, the negative charges in the wall are repelled (or pushed away). This leaves a positive charge on the wallboard at the spot where the balloon touches.

It is the attraction between the positively charged area of the wall and the negatively charged balloon that results in the balloon "sticking" to the board. Over time, electrons will transfer from the balloon to the wall, causing the balloon to become uncharged and fall to the floor.

Some materials lose electrons more easily than others. The more easily the material loses electrons, the better it will "charge up" the balloon.

Wool, cotton, and hair are the most effective materials to charge the balloons.

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.