1. Sound

2. Sound Travels as a longitudinal wave
Series of compressions and rarefactions
Anything that vibrates produces a sound

3. Speed of Sound Depends on properties of the medium
Elasticity, temperature, and density
Lower temperatures = slower waves
Some sounds are lower at some temperatures
Average speed is 343 m/s
Chuck Yeager flew at 293 m/s and is said to have flown faster than the speed of sound…how is this true??

4. He was at an altitude of 12,000 meters
Speed of sound at that height (lower temperature) is 290 m/s

5. Speed of Sound The speed of sound in air changes with temperature.
The speed at 0oC is 331m/s for dry air
It increases by 0.6 m/s for each degree Celsius above zero.

6. The speed of sound also depends upon the medium.
Sound needs a medium through which to travel. Sound cannot travel through the vacuum of space. Space is silent (no matter what you hear in the movies).
Sound travels faster through a solid and liquids than through air. WHY?
Proximity of particles and their movement

7. Elasticity and Density
Fastest through solids and slowest through gases
Solids are more elastic than liquids and gases
In 2 materials that are in the same state, sound travels fastest through the less dense subject.

8. Frequency and Pitch Pitch Depends on the frequency of the wave
How high or low a sound is
Depends on the frequency of the wave
High pitch = high frequency
Treble, a high soprano may have a frequency of 1000 Hz
Low pitch = low frequency
Bass, thunder has a frequency of 50 Hz

9. What can we hear????
Human ears can hear 20 TO 20,000 Hz
Hearing Test

11. Hearing and the Ear
Vibrations are amplified by the 3-bones in the middle ear ( that form a lever system ) to push waves into the inner ear (hammer/anvil/stirrup)
The inner ear ( basilar membrane vibrates  hair fibers stimulate nerve fibers that send impulses to the brain.
The brain interprets the impulse as sound.

14. ULTRASONIC Frequencies above 20,000Hz
Many animals can hear frequencies above this
Dogs = 35,000Hz
Cats = 65,000 Hz
Porpoises = 150,000Hz
Bats make ultrasonic sounds that echoes off of caves, etc.

15. Infrasonic Frequencies below 20 Hz Elephants communicate this way
Earthquakes, volcanoes, and some machinery gives off infrasonic sounds

16. The Doppler Effect
The change in wave frequency due to a moving wave source is called the Doppler Effect.
The Doppler Effect is observed when the source of sound is moving relative to the observer.

17. The Doppler Effect

18. Loudness & Intensity
Loudness is the human perception of sound intensity.
Intensity is the amount of energy in each wave.
Greater Energy = Greater Amplitude
Therefore, Intensity is determined by amplitude. Big wave = Loud
Small wave = Soft

19. Amplitude is related to Intensity
Characteristics
Loudness is related
to Amplitude
Amplitude is related to Intensity

20. Intensity Measured in dB 0 dB can barely be heard
Human ear has a pain threshold of 120 dB
Music above 85 dB can damage ears

21. The Decibel Scale

23. Acoustics Acoustics is the study of sound.
The effect produced by many reflections is called reverberation.
Soft porous materials and certain room shapes can reduce excess reverberation.
Acoustic scientists work on understanding human hearing and speaking.

24. COMBINING SOUNDS
CONSTRUCTIVE INTERFERENCE – SOUND WAVES COMBINE SO THAT RESULTING DISTURBANCE IS GREATER THAN EITHER SOUND WAVE WAS BEFORE
THIS IS WHY SOUNDS ARE LOUDER IN AMPIHTHEATERS – THE WAVES BOUNCE OFF THE WALLS AND COMBINE
DESTRUCTIVE INTERFERENCE – SOUND WAVES COMBINE SO THAT THE RESULTING DESTRUCTION IS SMALLER THAN EITHER WAVE WAS BEFORE
THE SOUND IS SOFTER
DEAD SPOTS ARE AREAS IN LARGE HALLS WHERE LITTLE SOUND CAN BE HEARD BECAUSE OF DESTRUCTIVE INTERFERENCE

26. Beats
A “BEAT” OCCURS WHEN 2 WAVES OF SLIGHTLY DIFFERENT FREQUENCY ADD TOGETHER - EVERY FEW CRESTS OR TROUGHS LINE UP
24-4 QUALITY AND SOUND

27. Sonar
SONAR IS HIGH-FREQUENCY ULTRASONIC WAVES THAT ARE USED IN A SYSTEM CALLED Sound Navigation And Ranging
RESEARCH SHIPS SEND SOUND WAVE INTO WATER THAT TRAVELS IN A STRAIGHT LINE UNTIL IT HITS AN OBJECT
THE WAVE IS THEN REFLECTED BACK TO THE SHIP
THE TIME IT TAKES TO TRAVEL BACK AND FORTH IS MEASURED AND USED TO CALCULATE THE DISTANCE TRAVELED
USED IN COMMERCIAL FISHING TO LOCATE FISH
USED TO FOCUS AUTO-FOCUS CAMERAS
USED TO FIND OIL MINERALS INSIDE THE EARTH

28. ULTRASONIC CLEANING
ULTRASONIC WAVES ARE USED TO CLEAN DELICATE ITEMS LIKE JEWELRY, ELECTRONICS, AND SURGICAL INSTRUMENTS.
THE VIBRATIONS KNOCK OFF DEBRIS WITHOUT DAMAGING THE ITEM

29. Sound and Medicine
ULTRASOUND IMAGING – ULTRASONIC WAVE IS SENT THROUGH THE BODY AND REFLECTS OFF BONES AND ORGANS
THESE ARE SAFER THAN X-RAYS, WHICH CAN ALTER CELLS
ULTRASONIC WAVES ARE ALSO USED TO TREAT PROBLEMS
USED TO BREAK UP KIDNEY STONES SO THAT THEY ARE EASIER TO PASS
USED TO TREAT INJURED MUSCLES

30. An echo is a reflected sound wave
Echoes
An echo is a reflected sound wave
An echo travels to a barrier and then reflects back
What materials are used to reduce echoes in buildings?
Acoustical tiles

31. Resonance - Demo
Resonance – when the frequency of the stimulus (wave) is the same as the object -
( material it is made of )
View: Tacoma Narrows Bridge Collapse
Fundamental Frequency – lowest frequency
possible of a harmonic series
Harmonics – ( also called Overtones) vibrations that are multiples of the fundamental frequency.

32. Harmonics and Overtones
1st harmonic = fundamental frequency
2nd harmonic = 1st overtone
3rd harmonic = 2nd overtone
4th harmonic = 3rd overtone
and so on...

33. Sound Interference – Interference of sound waves produce BEATS

34. Music vs. Noise You hear alternating loud and soft sounds.
Sound quality or timbre is the blending of pitches to produces sound
Music
Instrumental and vocal tones – sound waves in a structured or regular pattern
Noise
Sound waves with irregular vibration and no definite pattern

35. Standing Waves
Caused by the interference of two identical waves (or a wave and its reflected wave) travelling in opposite directions in a medium.
Wave pattern of alternating nodes and antinodes.
Nodes - areas of no displacement of the medium caused by destructive interference
Antinodes - areas of maximum displacement of the medium caused by constructive interference.
Note: One wavelength (shown in the diagram) is equal to twice the distance between nodes.
node
Antinode

36. Music
Pleasing quality, definite identifiable pitch, repeated time (rhythm)
All instruments create a vibration
String instruments – tighter string - higher pitch
Woodwind/brass instruments - column of air vibrates
Percussion – vibrates by being struck