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ALTERNATORS
Cars need electricity for their headlights, spark plugs, radios, and stereos that play deep thumping bass notes that can be heard a block away. Where do they get it? They aren’t connected to extension cords. The battery isn’t enough. Leaving the headlights on when the motor is off will discharge the battery after a few minutes. Automobiles and other vehicles carry their own small generators, called alternators.
WITH ADULT ASSISTANCE: When the engine is off, open the hood of an automobile. In the front of the engine you should be able to see the fan belts. One of these belts loops around an alternator, which is about as big around as your hand with your fingers spread out. The alternator is a small generator that contains the same kinds of parts as generators in power plants. Connected by the fan belt, the spinning motion of the engine spins the alternator.
The alternator keeps the battery charged. Battery power is handy for starting a car. When the key is first turned, an electric motor called a starter spins the engine for a few seconds to get it going. If the battery is dead, start looking for jumper cables!