1. Sound Pitch Loudness Sound Intensity Level Doppler Effect Physics Mrs. Coyle

2. Sound Sound is a longitudinal mechanical wave. Compressions(High Pressure) Rarefactions(Low Pressure)

3. Speed of Sound Depends on the medium. The more elastic the medium the faster sound will travel through it. Speed in metals>speed in water>speed in air Sound can’t travel through vacuum.

4. Speed of Sound in Air v = 331 + 0.6 T ( in meters/sec) T is the temperature in 0 C. In higher humidity, sound will travel faster.

5. Properties of Sound Reflection (Echo) Refraction Interference Diffraction

6. Pitch: the frequency of a sound wave. Musical notes have a given pitch. The note C has a frequency of 327Hz. When two notes differ by a ratio of 2:1 they are one octave apart. What would be the next higher C? (Ans:654Hz)

7. Bow (Shock) Waves Bow (Shock) Waves When the speed of a moving sound source is greater than the speed of the wave, a pressure ridge builds similar to the wave created by the bow of a ship. physlet animation

8. Sonic Boom When the pressure ridge of a bow wave of a jet passes over an observer on the ground, the observer experiences a sonic boom.

9. Doppler Effect The change in a wave's perceived frequency due to the motion of either the sound source or the observer. It is applicable to any type of wave. Austrian physicist Christian Doppler (1803-1853). train sound clip Simulations physlet animation http://www.walter-fendt.de/ph14e/dopplereff.htm

10. The Doppler Effect http://www.physicsclassroom.com/Class/sound/u11l3b.cfm

11. Doppler Effect Detected Frequency, (f D ) f D = f ( v±v o ) v±v s f : frequency of source v : speed of sound v o : speed of observer (+)when observer moving towards source v s : speed of source (-)when source is moving towards observer

12. Example 1 An ambulance is approaching a stationary observer. The siren of the ambulance emits a frequency of 480Hz and the speed of the ambulance is 50km/h(=13.88m/s). What frequency will the stationary observer hear when the ambulance is approaching? Assume T=20 o C. Answer: f d = 500Hz

13. Sound Intensity (I) I = (Power transmitted by the Wave)/Area Threshold of human hearing: I o =1 x 10 -12 Watts/m 2 Threshold of Pain: I P = 1 Watts/m 2

14. Sound (Intensity) Level A measure of our perception of the loudness of the sound. Unit: decibel(dB)

15. Sound (Intensity) Level, (decibel)  log I, unit for  is dB (decibel) I 0 The decibel compares the sound intensity (I), to I o (1 x 10 -12 Watts/m 2), the threshold of human hearing. Remember: log(10 x )= x

16. Examples of Sound Intensity Levels jet plane taking off140 dB air raid siren125 dB threshold of pain120 dB loud rock music115 dB ear damage starts 85 dB busy traffic 70 dB normal conversation 60 dB quiet library 40 dB soft whisper 20 dB threshold of human hearing 0 dB

17. Example 2 What is the sound level (decibel) of a sound of 10 -4 W/m 2 intensity ? Answer: 80dB

18. Example 3 How many times louder is a quiet library sound (40 dB) compared to a soft whisper (20 dB)? Hint 1: Property of logs: log(A/B) = logA –logB Hint 2: Take the difference in dB and then find (I 2 /I 1 ) Answer: (I 2 /I 1 )= 100/1