1. Chapter 16
Sound Waves

3. Sound is a wave.
A. Sound is a type of mechanical wave.
1. produced by a vibrating object and travels through matter
2. disturbances are vibrations-rapid back and forth motions
3. medium vibrates in the same direction as the wave travels and transfer energy
4. How Sound Waves Are Produced
a. started by vibrations that send out waves in all directions
Example: vocal cords- relax when you breathe to allow air to pass through the windpipe; they tense up when you are about to sing or speak

4. 5. How Sound Waves Are Detected
a. Shape of the ear (like a satellite dish) helps collect sound waves
b. Reflected into the ear canal (tiny tube)
c. Waves strike the eardrum ( thin skin-like membrane at the end of the ear canal) and they vibrate.
d. Vibrations transfer from the eardrum through the tiny bones in the middle ear (hammer, anvil and stirrup.)
e. Vibrations reach the cochlea (30,000 hair cells) and vibrate (bend) the tiny hairs causing the cells to send impulses along the nerves to the brain.
f. When your brain processes these signals, you HEAR A SOUND!

5. B. Sound waves vibrate particles.
1. You cannot see the motion of waves in air.
2. Imagine striking a drum:
a. Drum skin vibrates very rapidly (pushing in and out) and pushes against particles in the air. Particles become bunched together (compressions).
b. When the skin is pushed in the opposite direction, it leaves an open space for the particles to rush back in and fill it.
c. A listener hears all of these vibrations.

6. A vacuum is empty space and has no particles so
***A vacuum is empty space and has no particles so sound cannot travel through it!
C. The speed of sound depends on its medium.
1. Sound travels more slowly than light and at different speeds.
2. Two factors affect the speed of sound: type of medium and the temperature
3. The Effect of the Material
a. Sound waves travel faster through liquids than in air because liquids are denser (closely packed)
***Divers would hear a sound quicker underwater than people above water.
b. Sound waves travel through elastic solids as well.

7. 16.1 2. The Effect of Temperature
a. Sound travels faster through higher temperatures (hot air).
Example: Yelling outside on a hot day very a cold
winter morning
16.1

8. 16-2 Notes

9. Frequency determines pitch
Pitch depends on freq.
Pitch – high or low of sounds
High Freq. = short wavelengths = fast vibrations = High Pitch (and vice versa)

10. High and Low Frequencies
One complete wave is a cycle
Unit of measurement (frequency & pitch)
Hertz (Hz)
Human Hearing Range = 20 – 20,000Hz
Infrasound = > 20 Hz (elephants)
Ultrasound = < 20,000 Hz (dogs, bats, dolphins)

11. Natural Frequencies Frequency @ which object vibrates.
Constructive interference – when two waves of same natural frequency come together and add up to create higher sound (resonance)

12. Sound Quality Each musical instrument has special sound quality
Timbre (sound quality) – explained as combination of waves.
We hear fundamental tone.
Overtone – higher frequency pitches
Affected by starts & stops

13. Doppler Effect Ex. Pitch drops as ambulance passes you
1. Doppler Effect – change in a perceived pitch that occurs when the source of receiver a sound is moving.

14. Frequency & Pitch
Sound waves that hit your ear are closer together so pitch & freq. are higher.
As sound waves move away, they still hit your ear but are farther apart and lower in pitch.

15. 16-3 Notes

16. Intensity determines loudness
Intensity depends on amplitude
More energy = more intense and louder
Measured in decibels
So higher amplitude = high sound

17. Intensity can be controlled
Sound waves get weaker and weaker until sound is undetectable. (Amplitude goes down but freq. and pitch stay same)
Intensity is changed by adding or removing energy or changing amplitude. Ex. Muffler

18. Increases strength of electrical signal Ex. Adjust stereo volume
Amplification
Increases strength of electrical signal
Ex. Adjust stereo volume

19. Acoustics Scientific study of sound How sound is produced or received
How sound waves behave inside a space
Ex. Use of acoustic tiles to absorb or redirect waves

20. Damage to Hearing?
Sensitivity of hair cells in ear make it possible to hear but also easy to damage those hair cells.
Noises above 130 dB are dangerous and 140dB are very painful

21. 16-4 Notes

22. Sound has many uses Ultrasound waves used to detect objects
Ex. Babies
Echolocation
Sending out ultrasound waves and interpreting the returning sound echoes
Helps animals find their prey or objects in front of them.
Ex. Bats, Dolphins

23. Echolocation Bat Music Video

24. Sonar
Instruments that use sound waves (echolocation) to locate objects.
Sound navigation & ranging.
Send out ultrasound waves and use the echoes to produce an image on a screen.
Ex. Fishing Boats, Ships

25. Medical Uses
Examples: break up kidney stones, see used to clean medical equipment, to see inside internal organs, detect the movement of fluids (blood flow) through the body, checking the health of a fetus during pregnancy

26. Sound Waves and MUSIC!! Create clear pitches or rhythms.
natural frequencies.
Some have diff. parts that vibrate to make diff. pitches.
Stringed, wind, and percussion – 3 main types. **(electronic = 4th type)

27. Sound can be recorded and reproduced
Long distance voice communication
Translates then reproduces sound
Ex. Telephone
Recorded sound
Occurs in real time
Sound waves turned into electrical signals