doppler-shift-se-justin

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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) 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.

2019 Downloaded by Melk Kid (kidmelk@gmail.com) Activity B: Faster than the speed of sound Get the Gizmo ready :  Click Reset ( ).  Set f source to 300 Hz.  Check that v sound is set to 340 m/s. Introduction: On October 14, 1947, the Air Force test pilot Chuck Yeager became the first man to officially travel faster than the speed of sound in level flight. Modern fighter jets can fly nearly three times the speed of sound. Question: What happens when objects travel faster than the speed of sound? 1. Observe : Some jet planes can travel faster than the speed of sound. Place the observer below the road, and set the velocity of the plane ( v source ) to 500 m/s. Click Play . Observe for a while, and then click Pause . What do you notice? _ The plane is _ moving ahead of it's sound _ waves leaving them behind. 2. Make a sketch : Click Reset . The red circles represent every thousandth sound wave. To see more waves, turn on Display additional waves . Click Play and observe. Sketch the sound waves in the diagram at right. 3. Infer : Think about what the observer would experience as the jet flew by. Sorry, drawing on pdf escape wasn't as easy as I thought it would be. A. Describe what the observer would see and hear as the plane flew by. _ The observer would first see the plane fly by and then hear the sound of _ multiple sound waves hitting them _ at once. B. Supersonic aircraft produce a loud noise called a sonic boom . Look at the waves hitting the observer. Based on what you see, what causes a sonic boom? _ The sound waves from a _ cone. The person experiences the sonic boom when the come reaches her ears. C. At major sporting events in America, a flight squadron such as the Blue Angels often flies over the stadium in a tight formation at supersonic speeds. Would spectators in the stands hear the jet planes first or see them first? Explain your reasoning. _ They will see the jet planes before the here the them because they fly faster than the speed of _ sound and _ therefore will be in front o _ f their sound waves when flying.

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2019 Downloaded by Melk Kid (kidmelk@gmail.com) Activity C (continued from previous page) Now gather data to determine the effect of the sound source velocity. f source (Hz) v source (m/s) v sound (m/s) Frequency in front of source (Hz) Frequency behind source (Hz) Doppler shift magnitude 500 100 340 708 Hz 386 Hz 1.83 500 300 340 4243 Hz 266 Hz 16.0 Finally, gather data to see the effect of the speed of sound. (Note: The speed of sound in Earth’s atmosphere ranges from about 274 m/s to 355 m/s.) f source (Hz) v source (m/s) v sound (m/s) Frequency in front of source (Hz) Frequency behind source (Hz) Doppler shift 500 200 300 1499 Hz 300 Hz 5.00 500 200 500 833 Hz 357 Hz 2.33 4. Analyze : Look carefully at the Doppler shifts for each experiment. A. What effect did increasing the frequency of the sound ( f source ) have on the magnitude of the Doppler shift? _ The sound frequency had no effect on the doppler shifter. B. What effect did increasing the velocity of the sound source ( v source ) have on the magnitude of the Doppler shift? _ The faster the source is, the grater the shift. C. What effect did increasing the velocity of sound ( v sound ) have on the magnitude of the Doppler shift? The greater the velocity of _ sound is, the smaller the shift. 5. Think and discuss : Why did the magnitude of the Doppler shift increase as the velocity of the sound source increased, but decreased as the velocity of sound increased? If possible, discuss your answers with your classmates and teacher. _ The magnitude of the soppler shifter depends on how close the velocity o f _ the sound source is t o _ the velocity o _ f sound.