Vocabulary : Doppler shift, frequency, pitch, sonic boom, sound waves, wavelength
Highlight your answers in either GREEN / BLUE / OR YELLOW
Prior Knowledge Questions (Do these BEFORE using the Gizmo .)
Have you ever heard a siren on a moving ambulance, fire truck, or police car? If so, what happ...
Vocabulary: Doppler shift, frequency, pitch, sonic boom, sound waves, wavelength
Highlight your answers in either GREEN / BLUE / OR YELLOW
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
Have you ever heard a siren on a moving ambulance, fire truck, or police car? If so, what happens to
the sound as the vehicle passes by?
Sometimes when cars are passing I usually hear the car running and sometimes I hear the horn of the
car.
The change in the sound that you hear is called the Doppler shift.
Gizmo Warm-up
izmo illustrates why the Doppler shift occurs. The
The Doppler Shift G
Gizmo shows a vehicle that emits sound waves and an observer who will
hear the sounds.
1. Click the PLAY SAMPLE button ( ). (Check that the Gizmo’s sound
and your computer’s speakers are on.)
What do you hear?
I hear I police siren
2. Click Play ( ) and observe the sound waves emitted from the moving car. Click Pause ( ) and
compare the sound waves in front of and behind the car. What do you notice?
Something that I notice is the length between them is about 900cm
3. Use the Ruler to measure the wavelength, or the distance between the lines, of the waves in front of and
behind the car. (Note: The red circles represent every thousandth wave.)
Wavelength in front of car: _____600 cm______ Wavelength behind car: _____900 cm_______
Why do you think the waves in front of the car have a shorter wavelength than the waves behind the
car? I think that the reason that the front is shorter than the back is because the car is chasing the
waves and the waves in the back are running away from the car.
Get the Gizmo ready:
Activity A: ● Click Reset ( ).
● Check that fsource is set to 500 Hz and vsound is set
The Doppler shift
to 340 m/s, close to the actual speed of sound.
● Set vsource to
0 m/s.
, Introduction: The pitch of a sound, or how shrill or deep it is, is related to the frequency of the sound waves.
The greater the number of sound waves passing by a point each second is, the higher the frequency and the
pitch will be. The unit of frequency is the hertz (Hz).
Question: What causes the Doppler shift?
The reason that the doppler shifts is because the change of on how the car moves.
1. Observe: With the car’s velocity (vsource) set to 0 m/s, click Play. Notice the sound waves moving away from
the car in all directions.
A. Increase the frequency of the sound waves by moving the fsource slider to the right.
How does this affect the spacing of the waves?
The effect on the spacing of the wave is affected because the car still and its not moving so the
waves are just moving away.
When the wavelength of the waves is short, the sound will be high in pitch.
B. Now decrease the frequency by moving the fsource slider all the way to the left.
How does this affect the spacing of the waves?
The spacing of the waves are now farther apart because I lowered the source. And its creating less
waves.
Sound waves that are spaced far apart will produce a lower, deeper pitch.
2. Measure: Click Reset. Set the frequency (fsource ) to 1000 Hz. Change the velocity of the sound source
(vsource) to 200 m/s. (The car is now an airplane.) At upper right, turn on the Observed frequency (Hz)
checkbox.
Drag the observer onto the road. Click Play, and then click Pause when the sound waves first reach
the observer.
A. What is the frequency of sound waves in front of the plane?
The frequency is 2427.9
B. Click Play, and then click Pause just after the plane has passed the observer.
C. What is the frequency of sound waves behind the plane?
The frequency of the plan behind is 629.8
3. Summarize: Based on what you have learned, how will the sound that the observer hears change as
the airplane passes by? Explain your answer.
From what I learned I think that they way that the sound on what the absever hears is going change as the
airplane passes because it increases.
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