Electricity does not travel easily through certain materials like special rubber, plastic, and glass. These materials are known as "insulators" and they are used to keep electricity from leaving the wires it travels on. Insulators keep electricity in power lines. Glass, plastic or ceramic insulators high up on power poles keep electricity from traveling down the pole to the ground. If an insulator breaks, or a power line becomes disconnected from the insulators that hold it up, the line can fall to the ground and energize the area around it with a lot of electricity. If you touch a downed line-or even the ground near the line-you could be hurt or killed. If a power line falls on a car and you touch the car and the ground at the same time, you would also get a shock. Insulating materials also keep electricity inside appliance cords. Rubber or plastic insulation around the cords keeps the electricity in the wires and prevents you from getting a shock. If this insulation is broken or wears off, the electricity can come through and shock you. Also, if you overload an outlet by plugging in too many things, cord insulation can overheat and melt, causing a shock and fire hazard.   Next: Related Experiments Previous: Electricity Travels Through Conductors