In the previous section, you investigated how the Doppler effect works using an animation in the context of sound. In this section, you will further investigate the Doppler effect on sound.

Watch the following video and then answer the questions that follow. (Note: in the video you will hear a car horn as the car drives past the camera.)

What happens to the behavior of the waves in front of the car? Behind the car?

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The waves in front of the car bunch together and become more compact; the waves behind the car are spread further apart.

What happens to the pitch that you hear from the horn during the video?

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As the car passes by, the pitch lowers.

What happens to the actual frequency of the horn?

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The frequency of the horn itself is constant; the Doppler effect alters the pitch you hear.

The faster the sound source moves, the higher the apparent frequency becomes. If the speed of the sound source were to reach the speed of sound, the sound waves would get so compressed that they would form one large pressure wave called a sonic boom.

Watch another video showing the Doppler effect on sound.

As you have seen, the Doppler effect plays an important role in sound. In the next section, you will investigate the role of the Doppler effect on light.