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Doppler Shift Gizmo Physics (Avon Park High School) Name: Date: 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? As the vehicle passed by, the pitch of the sound goes lower. 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 (Oh. (Check that the Gizmo's sound and your computer's speakers are on.) What do you hear? The 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? jhe sound waves in front of the car are closer together than the sound waves behind 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? _| think since the car is moving towards the waves, the distance is shorter than the distance from the waves behind the car because it is moving away from those waves. Activity B: Get the Gizmo ready: Faster than the * Click Reset (2). speed of sound * Set feource to 300 Hz. * Check that Vsoung 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. Moder 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 (Vsouree) to 500 m/s. Click Play. Observe for a while, and then click Pause. What do you notice? The plane is ahead of the sound wave and the sound wave is near the tail of the plane 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. A. Describe what the observer would see and hear as the plane flew by. First, the observer would see the plane fly by and the sound from the various sound waves would hit them. 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 the cone shape 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 he planes fir: hey are faster than th f thi sound waves they emit. Activity C: Measuring the frequency change Get the Gizmo ready: ° Click Reset. Question: What factors affect the magnitude of the Doppler shift? 1. Observe: Using the Gizmo, try to determine how each factor (fsource, Vsource, ANd Vsouna) affects the observed Doppler shift. Based on what you have observed, how will each of these actions affect the magnitude of the Doppler shift? A. Increasing the frequency of the sound (fsource): Will cause the sound waves to be further apart. B. Increasing the velocity of the source (Vsource):Will increase the motion and speed of the car/plane C. Increasing the speed of sound (Vsouna): Will make the sound waves go faster 2. Measure: Set fsource to 500 HZ, Vsource to 200 m/s, and Vsouna to 340 m/s. Turn on Observed frequency, and drag the observer into the middle of the road. A. Click Play, and then click Pause just before the airplane reaches the observer. What is the frequency observed by a person in front of the airplane? 1214.3 Hz B. Click Play, and then click Pause just after the airplane has passed the observer. What is the frequency observed by a person behind the airplane? 314.8 Hz C. To measure the magnitude of the Doppler shift, divide the frequency of sound waves in front of the plane by the frequency behind the plane. What do you get? 3.857 Hz 3. Gather data: For each combination, measure the frequencies of the sound waves in front of and behind the moving sound source. Then divide the first number by the second number to calculate the Doppler shift magnitude. In the first experiment, find the effect of frequency. feource Vsource | Vsound | Frequency in front | Frequency behind | Doppler shift (Hz) (m/s) (m/s) of source (Hz) source (Hz) magnitude 300 200 340 728.6 188.9 3.857 1000 200 340 2428.6 629.6 3.857 (Activity C continued on next page) 
