Copy of DopplerShift

Name: Rameen Date: 9/12/22 Student Exploration: Doppler Shift Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. 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 is louder when it’s nearer but slowly gets low when as source moves farther away. 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? I hear a police car siren getting lower as the car moves away. 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 on the front and farther away/bigger on the back 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: 500 Wavelength behind car: 900 4. Why do you think the waves in front of the car have a shorter wavelength than the waves behind the car? I think they are shorter on the front because they bunch up on the front and then spread out Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

on the back. 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? the spacing gets shorter than before 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? the spacing gets bigger and the waves are farther away. 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? 2428.2 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? 629.7 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. The sound will be lower because the waves get bunched up on the front and then spread out to the back. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

The spectators would see the jet planes first and then hear them because they are causing sonic booms and move faster than the speed of sound. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved