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Sound: speed, Doppler effect. Sound wave density rarefaction densification pressure expansion compression Fluctuations: appr. 0.01%

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Presentation on theme: "Sound: speed, Doppler effect. Sound wave density rarefaction densification pressure expansion compression Fluctuations: appr. 0.01%"— Presentation transcript:

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 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?


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