1. Doppler Effect & Shock Waves

2. Doppler Effect
When a wave source is traveling with respect to an observer, the observer perceives a difference in frequency of the waves
This can be accomplished with a moving wave source or with a moving observer

3. Doppler Effect & Sound
If a moving sound source is coming toward you, the wave fronts are bunched together, so the wavelengths are shorter and you perceive a higher frequency or pitch
If a moving sound source is traveling away form you, the wave fronts are spread apart, so the wavelengths are longer and you perceive a lower frequency or pitch

4. Example
You are driving toward a parked emergency vehicle with its sirens on
As you approach the vehicle, the sound you hear will be… Why?
As you drive away from the vehicle, the sound you hear will be… Why?

5. Doppler Effect & Sound Is the sound frequency actually changing?
Is the wave speed changing?

6. Shock Waves
When the speed of the moving source is equal to or greater than the speed of the waves, a shock wave is produced

7. Shock Waves A shock wave produces a cone shape
When the source is moving faster than the wave speed, all of the wave fronts are behind the source

8. Sonic Boom
When a source producing sound waves travels faster than the speed of sound, the overlapping sound waves in the cone create regions of alternating very high and very low pressure which all reach the observer at one time, creating a loud boom
NOT only heard when speed of sound is
reached, but anytime the shockwave
cone reaches your ear.