doppler-shift-se-justin.docx

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2019 Downloaded by Melk Kid (kidmelk@gmail.com) Name: Justin L Date: 4/15/2024 Student Exploration: Doppler Shift Vocabulary: Doppler shift, frequency, pitch, sonic boom, sound waves, wavelength 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? _ the sound goes lower as the vehicle goes by. The change in the sound that you hear is called the Doppler shift . Gizmo Warm-up The Doppler Shift Gizmo illustrates why the Doppler shift occurs. The 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? _ T he sound goes from high to _ low. 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? _ The sound waves are closer in front of the car 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: 500m Wavelength behind car: 900m 4. Why do you think the waves in front of the car have a shorter wavelength than the waves behind the car? _ I _ think it's because the car is moving towards the waves in _ front of _ it _ and moving away from the waves

2019 Downloaded by Melk Kid (kidmelk@gmail.com) _ behind i _ t and therefore the distance between the waves is _ shorter in _ front than behind.

2019 Downloaded by Melk Kid (kidmelk@gmail.com) Activity A: The Doppler shift Get the Gizmo ready :  Click Reset ( ).  Check that f source is set to 500 Hz and v sound is set to 340 m/s, close to the actual speed of sound.  Set v source 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? 1. Observe : With the car’s velocity ( v source ) 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 f source slider to the right. How does this affect the spacing of the waves? _ They are closer together. When the wavelength of the waves is short, the sound will be high in pitch. B. Now decrease the frequency by moving the f source slider all the way to the left. How does this affect the spacing of the waves? _ They are farther apart. Sound waves that are spaced far apart will produce a lower, deeper pitch. 2. Measure : Click Reset . Set the frequency ( f source ) to 1000 Hz. Change the velocity of the sound source ( v source ) 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? _ 2428 Hz B. Click Play , and then click Pause just after the plane has passed the observer. What is the frequency of sound waves behind the plane? _ 6 2 9 Hz 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. _ As the plane passes by, the frequency changes from 2428 to _ 629 Hz and the change causes the pitch of the sound to _ change from hight to low.

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