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Title: The Doppler Effect
Principle(s) Investigated: List all principles that apply to this activity. Doppler Effect, Red Shift, Blue Shift, Big Bang Theory,
Standards : HS-PS4-1, HS-ESS1-2
Materials: Doppler Effect Buzzer
Procedure: Students
Student prior knowledge: Frequency, Wavelength, Speed of a wave.
Explanation: Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.
Teacher will demonstrate buzzer as it does not move. (1 min.)
Teacher will spin buzzer to demonstrate the differences between a moving sound wave and stationary sound wave. (2 min.)
Students will write down differences between a closer buzzer and a farther buzzer as teacher demonstrates buzzer.
In pairs, students will discuss why these differences occur, while the formula for speed, wavelength, and sound and definitions are displayed. (3 min.)
Teacher will launch into explanation for why this occurs and relate it to phenomena, then provide a summary of the major points. (10 min.)
Speed= wavelength/frequency
Speed of any wave is determined by characteristics of the medium, such as temperature and density.
Questions & Answers: Give three thought-provoking questions and provide detailed answers.
- How does the sound change as the buzzer moves closer or far away?
As the buzzer moves closer to you, the sound becomes higher pitched(higher frequency). As the buzzer moves farther away, the sound becomes lower pitched(lower frequency).
- Is the pitch higher or lower when it is closer to you than when it is not moving? What does that tell us about the frequency and wavelength?
The pitch is higher when it is closer to you than when it is not moving, since the waves become compressed. A higher pitch means a higher frequency and a lower wavelength since the speed of sound in air does not change.
- Is the pitch higher or lower when it is farther from you than when it is not moving? What does that tell us about the frequency and wavelength?
The pitch is lower when it is farther from you than when it is not moving, since the waves become elongated. A lower pitch means a lower frequency and a lower wavelength since the speed of sound in air does not change.
Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.
- Police Radar- A police officer uses radar, which detects the change in frequency between the emitted waves and the reflected wave to find the speed of a moving car. The police officer can then use this information to determine if the vehicle is speeding and write them a ticket.
- Sonic Boom- As a jet moves through the air, it produces sound waves, which compress towards the front and widen toward the rear (Doppler Effect). The sound waves are more compressed, the faster the jet moves. When a jet moves faster than the speed of sound, the waves merge into a single shockwave that can be heard as a boom from an observer on the ground as the shock wave passes them. Interestingly, the sonic boom cannot be heard by the pilot.
- Redshift/Big Bang Theory- Redshifting is the doppler effect applied to light. Light from galaxies as an indication that the universe is currently expanding. As stars move away from us they produce a longer wavelength, which means a higher frequency since the speed of light does not change. Stars moving away from us move towards the red side of visible light and are called “red-shifted.” The opposite is also true, when stars move closer to us, they produce a higher frequency that moves closer to the more energetic blue light, and are considered “blue-shifted.”
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.
https://www.pbs.org/video/unit-6-segment-c-doppler-effect-1fq3y8/
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