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Doppler Effect Lesson for Kids

Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Because of the Doppler effect, noises sound different as you move toward or away from a noisy object. Learn why the Doppler effect happens in simple terms.

What is The Doppler Effect?

I bet you've seen a magician pull a rabbit out of a hat, or a coin out of someone's ear. A magician will make you think something happened when it really didn't. The Doppler effect can also make you think something happened that didn't. It can make you think sounds change, when they don't.

Have you ever stood on the side of the road as a fast car drove past you? If you did, you might have noticed that as the car got closer to you, the sound of the car's engine got louder and sounded different. The car doesn't change its engine as it driving, so what's happening? The change in the way you hear a noisy object as it moves toward or away from you is called the Doppler effect.

The Doppler Effect Needs Movement

The Doppler effect happens because sound moves in waves, called sound waves.

Sound moves through the air in sound waves.
sound waves

Let's say you are visiting the fire station on a field trip when a fire call comes in. The first thing the firemen will do is turn on the alarm. That alarm sends waves through the air, just like a dropped pebble causes ripples on a pond.

As long as you don't move, the alarm will sound the same until it turns off. There is no Doppler effect going on because neither you nor the alarm are moving.

When the firemen are ready, they hop on their firetruck and turn on the siren. Now we will hear the Doppler effect because the object making the sound waves is moving.

If you're standing in front of the firetruck, the sound seems to get louder and quicker. That happens because the frequency of the sound waves get higher as the noisy truck comes toward you. Frequency is the rate at which the waves reach you. The sound waves in front of the firetruck bunch up, with less space between them. So the waves will reach you at a faster frequency, changing the way you hear the sound.

Imagine the red dot is a noisy firetruck. The sound waves in front of the truck are bunched together.
Doppler Effect

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