Doppler Effect with a Tuning Fork

A vibrating tuning fork is rotated on a string so that it alternately moves toward and away from the listener, causing a noticeable change in pitch that demonstrates the Doppler effect for sound.

1. Tie a strong string securely to the handle of the tuning fork.
2. Strike the tuning fork gently with a mallet to start it vibrating.
3. Hold the free end of the string and begin rotating the tuning fork in a vertical or horizontal circle.
4. Listen carefully to the sound as the tuning fork moves toward you and then away from you.
5. Observe the change in pitch during different parts of the rotation.

Doppler Effect (tuning fork) - WFU Physics Lecture Demonstrations:

Doppler Effect with Tuning Fork - Tony Verheyden:

📄 Doppler Turning Forks - Harvard Natural Sciences Lecture Demonstrations: https://old.physics.wfu.edu/demolabs/demos/3/3b/3B4018.html

📄 Doppler Turning Forks - Harvard Natural Sciences Lecture Demonstrations: https://sciencedemonstrations.fas.harvard.edu/presentations/doppler-tuning-forks

• Change the speed of rotation to increase or decrease the size of the pitch change.
• Use tuning forks of different frequencies to compare the effect.

• Ensure the string is securely attached to prevent the tuning fork from flying off.
• Keep a clear area around the demonstrator during rotation.
• Do not rotate the tuning fork near faces or fragile objects.
• Strike the tuning fork gently to avoid damage.

• Why does the pitch increase as the tuning fork moves toward you? (The sound waves are compressed, increasing the observed frequency.)
• Why does the pitch decrease as the tuning fork moves away? (The sound waves are stretched out, lowering the observed frequency.)
• Does the tuning fork itself change frequency while rotating? (No, only the observed frequency changes.)
• How is this demonstration similar to the sound of a passing siren? (Both involve a moving sound source creating a Doppler shift.)