1. Sound: speed, Doppler effect

2. Sound wave density rarefaction densification pressure expansion compression Fluctuations: appr. 0.01%

3. Speed of sound Compression waves Steel: Strong forces, high density

4. Speed of sound Compression waves Water Medium forces, small distances

5. Speed of sound Compression waves Air Nearly no forces, large distances Temperature dependent!

6. Classification Growing frequency 20 Hertz 20 000 Hertz=20kHz Audible range 3000 Hz best hearing Infra sound Ultra sound Growing Wave length? Earthquakes, heavy traffic Medical imaging, dog whistles, bats

7. Wave lengths of the audible range 20 kHz: 20 Hz: Width of a finger Width of a house Objects in our environment are of the same order of size as the wave length of sound waves.

8. Sound and hollow tubes Sound: transverse wave, compression wave node Loop at open end node Loop at open end Both ends open: One end closed:

9. Resonances of tubes Fundamental 1 st overtone Closed tubes open tubes

10. Human ear The human ear canal is a tube of approximately 3 cm length. Determine the fundamental frequency.

11. Doppler Effect

12. Resting sound source source at rest observer at rest Frequency f s Frequency f o V=340m/s

13. Sound source moving toward observer sourceobserver at rest Frequency f s Frequency f o Observer hears increased pitch (shorter wave length)

14. Sound source moving away from observer source observer at rest Frequency f s Frequency f o Observer hears decreased pitch (longer wave length)

15. Frequency heard by observer Source moving toward observer. Perceived wavelength: With Observer:

16. Observed frequency Observer moving at v o Source moving at v s 40m/s 20m/s rest 300Hz What do the car driver and the person hear?