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# Frequency and Pitch of Sound

## Explores how the frequency of a sound affects how we perceive it.

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How We Use the Doppler Effect

### How We Use the Doppler Effect

Credit: US Military
Source: http://commons.wikimedia.org/wiki/File:USMC-091125-M-2787C-393.jpg

In this photo, a military police officer is using a radar “gun” to check the speed of oncoming vehicles. Police radar is just one of the ways we use the Doppler effect.

#### News You Can Use

• The Doppler effect is a change in the pitch of a sound that occurs when the source of the sound is moving relative to the listener. It occurs because the frequency of the sound waves changes as the source of sound moves closer to or farther from the listener.
• The Doppler effect has several real-world applications. For example, besides police radar, the Doppler effect is used by meteorologists to track storms. Doctors even used the Doppler effect to diagnose heart problems.
• Credit: Dan
Source: http://www.flickr.com/photos/yodudedan/363045232/

A large Doppler weather radar located in central Illinois [Figure2]

• Watch this video to listen to the Doppler effect and see why it occurs:

#### Explore More

1. Describe what happens to sound waves from a car horn as the car approaches you. How is the sound affected by this change in the sound waves?
2. What is Doppler shift?
3. What are three real-world applications of the Doppler effect? How does each application use the Doppler effect?
4. What do all three of the applications in your answer to question 3 have in common?

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