Title: Scary Hair!
Objective: A person stands on a plastic stool and touches the sphere of a van der Graaf
generator. As charge accumulates on the sphere and their body, their hair begins to stand
up.
Purpose: To demonstrate the repulsion between like charges (and to have fun).
Materials: Find and borrow a van der Graaf static generator (middle schools and high
schools usually have one), a plastic stool (a one-step stool, about 30 cm tall), and a
grounding ball, stick, and wire.
Procedure: Place the van der Graaf generator at the edge of a table and put the plastic
stool a short distance away on the floor. The volunteer who will stand on the stool (for
electric insulation from the ground) should be able to reach out and touch the sphere of
the van der Graaf generator comfortably, but without coming too close to anything else,
particularly the base of the van der Graaf generator. Before the volunteer arrives, turn on
the van der Graaf generator and touch the grounding ball to the van der Graaf generator's
sphere to eliminate any charge from its surface. Have the volunteer stand on the stool (it's
not a matter of how tall they are—they need the electric insulation that the stool provides)
and touch the sphere of the van der Graaf generator. They should feel absolutely no shock
while they’re doing this because you are still grounding the sphere. When the volunteer
is ready and not near anything besides the sphere and the stool, move the grounding ball
away from the van der Graaf generator's sphere. Never move the grounding ball back to
the van der Graaf generator's sphere while the person is still touching the sphere because
the volunteer will feel a shock. As charge accumulates on the sphere and the volunteer,
that person's hair will begin to stand up. Some people's hair works better than others and
there is simply no predicting whose hair will work best. It's completely trial and error!
The only exception to that rule is with children—young children with fine, straight,
white-blond or jet black hair always work well.
Science Behind It: The charge that migrates onto the volunteer's body through their
conducting skin also works its way onto their hairs. When each hair is sufficiently
charged, the Coulomb repulsions between the hairs lift them upward against their own
weights.