Doppler Ball
Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required
Categories: Astronomy and Space, Electromagnetic Spectrum and Waves, Sound
Alternative titles: Sound Shifts with Motion
Summary
A Doppler ball contains a speaker that emits a constant tone. When the ball is thrown or swung on a string, the pitch of the sound changes due to the Doppler Effect, demonstrating how relative motion alters perceived frequency.
Procedure
- Turn on the Doppler ball so it emits a continuous tone.
- Have two people play catch with the ball, listening to the change in pitch as it moves toward and away from each person.
- Attach the ball to a string and swing it in circles above your head.
- Observe how the pitch rises as the ball moves toward you and lowers as it moves away.
- Discuss how the same principle applies to other wave types, such as water waves and light waves.
Links
Demonstrate the Doppler Effect in Your Classroom | Doppler Ball - Arbor Scientific:
doppler example in the classroom - PhysicsHigh:
📄 DOPPLER BALL - Corridor Physics: https://physics.anu.edu.au/engage/outreach/_files/Doppler%20Effect.pdf
Variations
- Record the sound of the Doppler ball in motion and analyze frequency shifts with audio software.
- Compare the Doppler shift when throwing the ball slowly versus quickly.
- Swing the ball or a speaker around to show a similar effect.
- Relate the activity to real-world examples such as ambulance sirens or speeding cars.
Safety Precautions
- Ensure the play area is clear of obstacles when throwing or swinging the ball.
- Do not swing the ball near people to avoid hitting them.
- Securely fasten the string to the ball before swinging to prevent accidents.
- Handle the battery-operated component carefully and keep away from water.
Questions to Consider
- Why does the pitch of the ball sound different when it is moving toward versus away from you? (The frequency of sound waves increases when approaching and decreases when receding due to the Doppler Effect.)
- How would the sound change if the ball moved faster? (The pitch shift would be greater because the frequency change is proportional to speed.)
- Where do we encounter the Doppler Effect in everyday life? (Ambulances, trains, police sirens, moving cars, astronomical observations.)
- Does the Doppler Effect only apply to sound? (No, it also applies to all types of waves, including light and water waves.)