Van de Graaff Flying Ball and Silver Snake

Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff

Categories: Van de Graaff Generator

Alternative titles: Electrostatic Floating Ball, Dancing Silver Snake

Summary

A metallized ball or a metallic ribbon (the "silver snake") placed near the dome of a Van de Graaff generator demonstrates electrostatic induction and repulsion. The ball, once charged, floats at a distance from the dome, while the ribbon repeatedly touches and recoils, creating a dynamic “dancing” effect.

Procedure

Set up the Van de Graaff generator in an open area.
Attach a lightweight metallized ball (such as a pith ball covered in foil) to a string so it can move freely.
Bring the ball close to the charged dome. It will be attracted by induction, touch the dome, gain charge, and then be repelled, floating at a distance.
Next, place a thin metallic ribbon (the “silver snake”) so that it can drape toward the dome.
As the dome charges, the ribbon will be attracted, touch the dome, become charged, and then be repelled. Unlike the ball, it quickly loses charge to the air and strikes back repeatedly, creating a fluttering motion.
When finished, discharge the dome with the grounding rod.

Links

Flying Ball and Silver Snake - Shethar Davis:

Variations

Use different materials for the ball (foil-covered paper, ping pong ball, Styrofoam) to compare how well they hold charge.
Try ribbons of different lengths and materials to vary the “dancing” motion.
Place both the ball and the ribbon near the dome at the same time for a combined effect.

Safety Precautions

Always discharge the Van de Graaff dome with a grounding rod before and after use.
Ensure participants do not touch the dome while it is charged.
Keep the apparatus away from flammable materials and sensitive electronics.
Do not operate in very humid environments, as this can lead to unpredictable sparks.

Questions to Consider

Why does the ball remain repelled after touching the dome, while the ribbon returns?
How does induction cause the ball and ribbon to first be attracted?
What role does air conductivity play in discharging the ribbon so it strikes back repeatedly?
How is this related to natural phenomena, like lightning striking and discharging repeatedly?
What would happen if you used an insulating material instead of a conductor for the ball or ribbon?