5.36. Doppler Effect http://www.ck12.org
FIGURE 5.72
Experiencing the Doppler Effect
As the car approaches listener A, the sound waves get closer together, increasing their frequency. This listener
hears the pitch of the siren get higher. As the car speeds away from listener B, the sound waves get farther apart,
decreasing their frequency. This listener hears the pitch of the siren get lower. You can experience the Doppler effect
with a moving siren in the following animation: http://www.epicphysics.com/physics-animations/doppler-effect-ani
mation/
Q:What will the siren sound like to listener A after the police car passes him?
A:The siren will suddenly get lower in pitch because the sound waves will be much more spread out and have a
lower frequency.
Summary
- The Doppler effect is a change in the frequency of sound waves that occurs when the source of the sound
waves is moving relative to a stationary listener. - As the source of sound waves approaches a listener, the sound waves get closer together, increasing their
frequency and the pitch of the sound. The opposite happens when the source of sound waves moves away
from the listener.
Vocabulary
- Doppler effect: Change in the frequency and pitch of sound that occurs when the source of the sound is
moving relative to the listener.
Explore More
At the following URL, observe the Doppler effect in the animation and then answer the question. Check your answer
by reading the “Discussion” section of the Web page. http://www.ndt-ed.org/EducationResources/HighSchool/Soun
d/dopplereffect.htm