Static tubes

Materials

• Clear plastic tubes with end caps
• Styrofoam peas (filling from bean bag chairs) or tiny broken-up pieces of Styrofoam pellets
• Empty bowl, shoe box, or large can
• Wool cloth

Background

This activity will be most instructive if taught following other activities that involve experiences with induced charge such as Dancing Paper Bunnies and What Will a Charged Balloon Attract?

The plastic tube, when rubbed with wool, picks up electrons and becomes negatively charged. This induces a positive charge in the Styrofoam peas which will cling to the plastic, pick up electrons, and later leap away.

When your finger approaches the negatively charged tube, the finger becomes positively charged by induction, just like the Styrofoam peas. Therefore, your finger and the Styrofoam have like charges, and you will find that you can chase the peas around inside the tube by moving your finger on the outside.

Procedure

• If you can tolerate the possibility of having Styrofoam peas floating around in your classroom, your students will have a wonderful time making their own static tubes. You may find it works well to set up one corner of the room in which students will come to make their static tubes in small groups.
• Give each student a clear plastic tube and two end caps. Have them insert one cap into one end of the tube.
• Place all of the Styrofoam peas inside a large container such as a bowl, shoe box, or can. Challenge the students to get about two tablespoons of Styrofoam peas inside their static tubes through the end that they have left uncapped. This is not always easy, because the plastic tubes take on a charge with minimal handling and will attract and repel the Styrofoam peas.
• When the students have placed their peas inside the tube, have them insert the other end cap, and remove any Styrofoam clinging to the exterior of the tube with a cupped hand. Rub the exterior of each tube with the wool cloth.
• Let the students experiment with their closed static tubes. Can they pour all of the peas from one end to the other? How can they move any peas along that seem to be stuck? Using terms they have learned through other activities, such as attract, repel, static charge, and induction, can they describe what happens when they bring a finger close to the outside of the tube?