2. Properties Of Sound Sound waves are produced as longitudinal waves by compressions and rarefactions in matter. The medium for sound waves can be solid, liquid or gas.

3. Properties Of Sound Compression: An area of density greater than the actual density of the medium Rarefaction Rarefaction: An area of density less than the actual density of the medium

4. Properties Of Sound These alternating pressure changes cause the eardrum to vibrate.

5. Speed of Sound The speed of sound depends on temperature and density of the medium. Speed of sound in various media: air – 331.6 m/s ± 0.6 m/s/ o C water – 1498 m/s ± 2.4 m/s/ o C steel – 3225 m/s

6. Doppler Effect A change is the apparent frequency of sound when the source and listener are in motion relative to each other. When they are moving toward each other, the frequency appears to be higher. When they are moving apart, the frequency appears to be lower.

7. Doppler Effect If the source of sound is moving, the waves in front are compressed and the waves behind are elongated. If the listener is moving, they encounter more waves as they approach the sound and fewer waves as they leave it.

8. Doppler Effect

9. Doppler Radar Doppler radar uses the same change in wavelength to determine the direction and speed of an approaching storm. Police radar uses the Doppler Effect to measure the speed your car is traveling.

10. Resonance Every object has a natural frequency If something vibrating at the same frequency disturbs it…. It will vibrate, too!!

11. Examples of Resonance

12. Human Hearing Sound waves enter the ear and the compressions push the eardrum as the rarefactions pull the eardrum. Three bones convert the motion to pulses in the inner ear that stimulate nerve fibers which are converted to sound in the brain. The human ear can detect wave vibrations with a frequency range from 20 Hz to 20,000 Hz.

13. Sound Intensity The intensity of a sound wave is a measure of its amplitude or loudness. The SI unit for sound intensity is the decibel or dB. This is a logarithmic scale where each 10 dB is 10 times louder than the next lower value.

14. Table of Decibel Ratings Jet airplane takeoff150 dB Jackhammer130 dB Threshold of Pain120 dB Rock Concert110 dB Screaming baby 90 dB Busy Street Corner 70 dB Normal Conversation 60 dB Buzzing Mosquito 40 dB Whisper 20 dB Pin Drop 10 dB Threshold of Hearing 0 dB Sound Intensity

15. The intensity of sound or decibel is compared to the threshold of hearing. The intensity of sound at the threshold of hearing is 10 -12 W/m 2. If the sound intensity is 50 dB, then I for intensity is 10 -7 W/m 2.

16. Sample Problem The intensity of sound is measured to be 10 -8 W/m 2. What is the intensity in decibels? β = 10 log (10 -8 W/m 2 / 10 -12 W/m 2 ) = 10 log (10 4 ) = 10 (4) = 40 dB = 10 log (10 4 ) = 10 (4) = 40 dB

17. Beats The “beats” are the intensity variations in the resulting wave These waves differ by 1 Hz…. These waves differ by 3 Hz….

18. Beats The “beats” are the intensity variations in the resulting wave These waves differ by 1 Hz…. These waves differ by 3 Hz….

19. Beats The “beats” are the intensity variations in the resulting wave These waves differ by 1 Hz…. These waves differ by 3 Hz…. What about these waves???....