Book 14, Question 79
Why Does a Siren Sound Higher as It Comes Toward You and Lower as It Goes Away?
A siren sounds higher as it comes toward you because the sound waves get squeezed together! After it passes, the waves are stretched out. This is called the Doppler effect.
More fun facts
- Waves, such as sound waves, change when their source is moving toward or away from you.
- When a car with a siren moves away, its sound waves get stretched out, making a lower pitch.
- After the siren passes you, its sound waves seem longer.
- Fewer waves reach your ear each second from a sound moving away.
- To notice the effect, the sound has to be moving toward or away from you at about 15 to 20 miles per hour or more.
Sources: Exploratorium, Science News Explores, Science News Explores, BBC
Questions kids ask
Does the siren really change its sound?
No. The siren makes the same sound the whole time. Its sound waves just get squished together as it comes toward you and stretched out as it moves away.