Doppler EffectMoving Source

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

Doppler Effect Relative motion creates a change in

frequency

HowStuffWorks Videos "Assignment Discovery: Doppler Effect”

Doppler fire engine

Doppler Effect

Halloween Costume?

Big Bang Theory Clip

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

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.

Practice

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?

Math

Source moving towards observerfo = v•fs/(v-vs)

Source moving away from observer fo=v•fs/(v+vs)

Math PracticeA 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?

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?

Math Practice

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.