What Will a Charged Balloon Attract?

Materials

• Balloons
• Styrofoam packing pellets or puffed rice cereal
• Wool cloth
• Salt and pepper (loose tea can be substituted for pepper) the tiny packets of salt and pepper from fast food restaurants are perfect

Background

A balloon rubbed with a wool cloth becomes negatively charged. When this balloon is held a few inches above a pile of Styrofoam pellets, the neutrally charged pellets become positively charged by induction and leap upward to cling to the balloon. After several minutes, some of the electrons may drain off the balloon onto the pellets. This will cause the pellets to become negatively charged and be repelled by the balloon. When this happens they may actually leap off the balloon and back to the table. The repelled Styrofoam pellets may then transfer their excess electrons to the table after a few minutes and once again leap toward the balloon. Grains of salt and pepper will react toward a charged balloon in much the same way, resulting in an amazing (if small-scale) display.

Procedure

• Give each student a balloon and a handful of Styrofoam pellets. After the students have inflated and tied off their balloons, rub the surface of each balloon with a wool cloth.
• Now have the students bring the balloons close to the Styrofoam and observe what happens. After the Styrofoam clings to the balloon, students who are patient and wait several minutes may see some of the Styrofoam leap forcibly away from the balloon back to the table.
• After the students have experimented with the Styrofoam and balloons, have them predict what might happen if a charged balloon is held a 2 - 3 inches above a pile of salt and pepper.
• Give each student a small pile (1/4 teaspoon) of mixed salt and pepper on his or her desk, recharge the balloons with the wool cloth, and let them do an experiment to find out. Students who observe very closely will notice that the same grains of pepper and salt will alternately leap toward and away from the balloon.