Charging two different materials using a wool cloth

Different materials have different amounts of attraction for electrons. When two objects rub against each other it is likely that one will steal electrons from the other.

	When wool is rubbed against a PVC (a type of plastic) strip, the PVC steals electrons from the wool because it has a greater attraction for electrons than wool does. The PVC strip ends up with a negative charge while the wool ends up with a positive charge. Since PVC is a good insulator, the charges stay where they are placed. They will remain there until someone handles the surface of the strip (grounding it) or until particles in the atmosphere steal the charge from it.
	When wool is rubbed against a Nylon strip (another type of plastic), the wool will steal electrons from the Nylon because wool has a greater attraction for electrons than Nylon does. As a result, the Nylon ends up positively charged and the wool ends up negative. Since Nylon is a good insulator, the charges will also stay where they are placed. They will remain there until someone handles the surface of the strip (grounding it) or until particles in the atmosphere steal the charge from it.
	After the two strips have been charged by rubbing them with wool cloth, if they are brought near each other, there is a force of attraction which pulls the two strips together. If the two strips had like charges, they would repel each other and move apart. By experimenting with just the plastic strips and the wool it is impossible to tell which one is positive and which is negative. (unless you've seen the animations)