Does the same sound always sound the same?

It’s hard not to stop what you’re doing and watch when a fire truck comes barreling down the road with its sirens blaring. But once the truck passes, something strange occurs: the sound of the siren changes pitch. Why is that?

In this lesson, students come up with equations in several variables to explore the **Doppler Effect**, which explains how sound from a moving object gets distorted. Along the way, they’ll explore the relationship between the wavelength, frequency, and pitch of a sound, and will also explore what happens when an object breaks the sound barrier.

- Explore the relationship between frequency, wavelength, and pitch of a sound
- Write an equation for wavelength in terms of frequency for the sound emitted by a stationary object
- Describe how the frequency of sound emitted by a moving object will appear different to stationary observers in front of and behind the object two observers
- Write a formula for the observed wavelength of a sound wave in terms of the wave’s actual frequency and the speed of the object emitting the sound
- Write a formula for the observed frequency of a sound wave in terms of the wave’s actual frequency and the speed of the object emitting the sound
- Describe how observers will experience sound emitted from an object as it moves past the speed of sound

Christian Doppler