1. THE DOPPLER EFFECT Section 9.5

2. Key Terms  Doppler Effect

3. Doppler Effect  As an emergency vehicle approaches, the pitch (frequency) of the siren changes.  As the siren approaches you, the waves are compressed and the sound entering your ear is of a higher frequency than the sound generated by the siren.  As the siren moves away from you, the opposite occurs and the sound entering your ear is of lower frequency than the sound generated by the siren  Doppler Effect

4. For Example…

6. Sheldon’s Take

7. Doppler Effect Cont’d  Not all moving sources of sound will generate a Doppler effect.  Speed of moving source must be a reasonable fraction of the speed of sound. Emergency vehicle moves ~ 30 m/s Speed of sound ~ 332 m/s Therefore  Vehicle moves at ~ 10% speed of sound

8. Calculating the Doppler Effect  Where  f obs = frequency of observer  v sound = local speed of sound  v detector = speed of detector  v source = speed of source  f 0 = frequency of source

12. Summary

13. Homework  Page 435  Questions 1-7