Charged balloon showing electrostatic attraction of polystyrene beads.

This transparent balloon has been charged using a balloon pump. Inside, it contains hundreds of lightweight polystyrene beads. When the balloon is inflated rapidly, the beads are thrown around inside and rub against the inner latex surface. This friction causes a build-up of static electricity: the beads all gain the same charge, so they repel each other. At the same time, the balloon’s inner surface develops the opposite charge, attracting the beads and causing them to stick to the inside wall. This simple and exciting demonstration beautifully shows how like charges repel and opposite charges attract—a foundational concept in electrostatics.