1. Doppler Effect
Moving Source

2. Warm Up on Pear Deck
High pitched sounds have relatively large _______ and small _______.
As the frequency of a sound increases, the wavelength _______ and the period_______
When the frequency of a forced vibration approaches the natural frequency of a vibrating object, the vibration in the object increases its
A woman standing on a train platform listens to a train as it approaches her at a constant speed. The train engineer blows the whistle of the train, which produces a frequency of 450 Hz. As the train approaches the woman on the platform, she will hear the frequency (pitch) of the whistle as

3. Doppler Effect Relative motion creates a change in frequency
HowStuffWorks Videos "Assignment Discovery: Doppler Effect”
Doppler fire engine

4. Doppler Effect

5. Halloween Costume?
Big Bang Theory Clip

6. Doppler Example
A student sees a train that is moving away from her and sounding its whistle at a constant frequency. Compared to the sound produced by the whistle, the sound observed by the student is
(1) greater in amplitude
(2) a transverse wave rather than a longitudinal wave
(3) higher in pitch
(4) lower in pitch

7. Practice
Choose the letter of each statement about the Doppler Effect that is true.
a. It occurs when a wave source moves towards an observer.
b. It occurs when an observer moves towards a wave source.
c. It occurs when a wave source moves away from an observer.
d. It occurs when an observer moves away from a wave source.

8. Practice
Two fire trucks with sirens on speed towards and away from an observer as shown below.
a) Which truck produces a higher than normal siren frequency?
b) Which truck produces a lower than normal siren frequency?

9. Math Source moving towards observer fo = v•fs/(v-vs)
Source moving away from observer
fo=v•fs/(v+vs)

10. Math Practice
A police car is moving toward a stationary observer at 15 m/s and its siren is sounding at 800 hz. What frequency will the observer hear is the speed of sound in 341 m/s?
From the previous problem, what frequency would the observer hear after the car passes if it continues at the same speed?

11. Math Practice
While standing near a railroad crossing, a person hears an approaching train horn at 440 Hz. The train is traveling at 20.0 m/s and the speed of sound is 346 m/s.
What is the actual frequency emitted by the horn?

12. Math Practice - challenge problem
A car approaching a stationary observer emits 450. Hz from its horn. If the observer detects a frequency of 470. Hz, how fast is the car moving? The speed of sound is 343 m/s.