1. Sound Origin of Sound Nature of Sound in Air Media that Transmit Sound
Speed of Sound in Air
Refraction
Energy in Sound Waves
Forced Vibrations
Natural Frequency
Resonance
Interference
Beats

2. Sound... ...a longitudinal wave in air caused by a vibrating object.
Sound requires a medium.
solid, liquid or gas
Will a bell ring in a evacuated Bell Jar?

3. Nature of Sound in Air
Sound waves have compression and rarefaction regions.

4. Origin of Sound infrasonic ultrasonic human hearing range
frequencies < 20 Hz
ultrasonic
frequencies > 20,000 Hz
human hearing range
frequencies between 20 Hz and 20,000 Hz

5. Speed of Sound in Air
340 meters/second
760 miles/hour
Mach 1

6. SPEED OF SOUND increases with humidity How it varies:
increases with temperature
increases with density
How it varies:

7. Lightning and Thunder
What is the approximate distance of a thunderstorm when you note a 3 second delay between the flash of the lightning and the sound of the thunder?

8. What is the approximate distance of a thunderstorm when you note a 3 second delay between the flash of the lightning and the sound of the thunder?
Answer: 3 seconds  340 meters/second
= 1020 meters

9. Acoustics... ...the study of sound properties.
When a sound wave strikes a surface it can be.…
(a) reflected.
(b) transmitted.
(c) absorbed.
(d) all of these.

10.  Acoustics... ...the study of sound properties.
When a sound wave strikes a surface it can be.…
(a) reflected.
(b) transmitted.
(c) absorbed.
(d) all of these. 

11. Reflection of Sound e.g. an echo
Reverberation - re-echoed sound, multiple reflections of sound waves from walls
Compare reflections from a hard wall with that from a carpet wall.

12. Refraction of Sound Refraction - the bending of a wave
Sound travels faster in warm air than in cool air.
Sound waves bend toward cooler air.

14. Speed of Sound Subsonic - slower than the speed of sound
Supersonic – faster than the speed of sound
speed of object
Mach Number =
speed of sound

15. Forced Vibrations/Resonance
…the setting up of vibrations in an object by a vibrating force.
Examples of Forced Vibration:
A tuning fork touching a wood surface
Sounding boards for stringed instruments
Matching tuning fork boxes

16. During forced vibration sound is intensified because a larger surface area is available to vibrate air molecules.

17. Resonances

18. Sound Interference
Overlapping compressions of a sound wave will result in…
…constructive interference.
…and a louder sound.
Overlapping a compression and a rarefaction results in...
…destructive interference.
…and a softer sound.

20. Destructive Interference
Constructive Interference

21. Noise reduction headphones Echo cancellation
Sound Interference
Noise reduction headphones
Echo cancellation

22. Beats
Beats - the periodic variation in loudness of two sounds played together
The beat frequency is equal to the difference in the frequency of the two sounds.

23. For the same temperature for air, does sound travel faster in humid Galveston or in dry El Paso?
(a) Galveston
(b) El Paso
(c) same speed in either city

24. For the same temperature for air, does sound travel faster in humid Galveston or in dry El Paso?
(a) Galveston
(b) El Paso
(c) same speed in either city

25. The bending of sound through air of uneven temperature is called
(a) reflection
(b) refraction
(c) interference
(d) reverberation
(e) resonance

26. The bending of sound through air of uneven temperature is called
(a) reflection
(b) refraction
(c) interference
(d) reverberation
(e) resonance 

27. Lightning is seen, then ten seconds later thunder is heard
Lightning is seen, then ten seconds later thunder is heard. Approximately, how far away in meters is the thunder cloud?
(a) 10,500 m
(b) 5280 m
(c) 1050 m
(d) 3400 m
(e) 680 m

28. Lightning is seen, then ten seconds later thunder is heard
Lightning is seen, then ten seconds later thunder is heard. Approximately, how far away in meters is the thunder cloud?
(a) 10,500 m
(b) 5280 m
(c) 1050 m
(d) 3400 m
(e) 680 m 

29. A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating near each other. How many beats per second are heard?
(a) 255
(b) 510
(c) 10
(d) 250
(e) 260

30. A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating near each other. How many beats per second are heard?
(a) 255
(b) 510
(c) 10
(d) 250
(e) 260 

31. Musical Sounds

32. Noise Versus Music What is the difference between noise and music?
Answer: The appearance of the waveform.
Mac Mic

33. NOISE VERSUS MUSIC

34. Same Note - Different Instrument

35. Fundamental Frequency
Harmonic
a partial tone that is an integer multiple of the fundamental frequency
Fundamental Frequency
the lowest frequency of vibration
a.k.a. the first harmonic

39. Back

40. Sound Intensity and Loudness
Intensity of Sound
refers to the amplitude of the pressure variations in the sound wave

41. Loudness
the physiological sensation directly related to the sound intensity
measured in bels
1bels = 10 decibels

42. Loudness
A sound of 10 decibels is or 101 or 10 times as intense as 0 decibels.
20 decibels is 102 or 100 times the intensity 0 decibels.
How much more intense is sound at 100 dB than sound at 50 dB?
Answer: times

43. Source of Sound Loudness (db)
Threshold of Hearing 0
Conversation 60
Ear Damage Begins
Amplified Music
Jet Airplane at 30 meters 140

44. Common Sound Intensities