1. Chapter 21: Sound
Pages 532 - 557

2. • Sound is a form of energy produced by the
vibration of matter.
• Sound is a compressional or longitudinal wave
• Sound is transmitted through solids, liquids,
and gases.

3. • Sound is transmitted better through
solids and liquids. Why?
–More dense
• Gases transmits sound a lot farther
than a solid and liquid. Why?
–Less dense; not as many
particles to interfere.

4. Sound
• So what causes sounds to travel better
through some substances and not
others?
–The greater the elasticity, the
greater the speed.
–The greater the density, the slower
the speed.
–The best conductors of sound are
elastic substances.

5. • Sound can not be transmitted
through a vacuum.
–Sound needs a medium in order
for it to be transmitted.
• Radio waves can travel through a
vacuum; no medium is needed.
–This is why astronauts can use
radio signals to talk in space.

6. Speed of Sound
• 344 m/s in air at 20°C
• Depends on:
– Type of medium
• travels better through liquids and solids
• can’t travel through a vacuum
– Temperature of medium
• travels faster at higher temps

7. The denser the medium, the
faster sound will travel.
The higher the temperature, the
faster the particles of the
medium will move and the faster
the particles will carry the sound.
Sound travels through different media.
We hear sound which usually travels through air. Sound
travels through other media as well, such as water and
various solids.
Sound travels different speeds in different media. Sound
typically travels faster in a solid that a liquid and faster in
a liquid than a gas.

8. Parts of the ear
• Outer ear: pinna
• Ear canal
• Ear drum: tympanum
–Vibrates the ear drum

9. • Middle ear: three small bones
–Anvil
–Hammer
–Stirrup
• Inner ear
–Cochlea: filled with fluid
•Hair-like nerve endings
•Auditory nerves

10. Brain
• Damage done to the hairs
causes permanent hearing
loss. The hairs never grow
back.

11. B. Human Hearing
sound wave
vibrates ear drum
amplified by
bones
converted to
nerve impulses in
cochlea

12. Human Hearing
• Pitch
– highness or
lowness of a
sound
– depends on
frequency of
sound wave
– human range: 20
- 20,000 Hz
ultrasonic waves
subsonic waves

13. FREQUENCIES YOU CANNOT HEAR
•Ultrasonic: higher than 20,000 Hz
Uses: clean jewelry, medical
applications
•Infrasonic: lower than 20 Hz
Found: in the atmosphere and
in the crust when plates move; also
an indication motion sickness

14. Human Hearing
• Intensity
– volume of sound
– depends on energy (amplitude) of sound wave
– measured in decibels (dB)

15. Human Hearing
70
80
100
110
120
40
18
10
0
DECIBEL SCALE
Above 120 dB can cause hearing loss

16. Doppler Effect
• Doppler Effect
– change in wave frequency
caused by a moving wave source
moving toward you -
pitch sounds higher
moving away from you
- pitch sounds lower

17. What is the Doppler Effect?
The Doppler Effect is the apparent change in frequency
detected when the sound is moving relative to the
hearer.

18. Reflection of Sound Waves
• Echoes
• Echolocation: process using reflected sound
waves to find objects
– Bats
– Whales
– SONAR
– Ultrasonography

20. Seeing with Sound
• Ultrasonic waves - above 20,000 Hz
Medical Imaging SONAR
“Sound Navigation and Ranging”

21. What is sonar?
Sonar is a system that uses the reflection of underwater
sound waves to detect objects. This has been used to
find sunken ships and schools of fish.

22. Diffraction
• Bends of waves around or through a barrier
Examples:
1. Thunder
2.Someone in the hallway
on the other side and we
can hear them.

23. Constructive - louder
D. Interference
• Interference
– the ability of 2 or more waves to combine to form a
new wave
Destructive - softer

24. D. Interference
• Beats
– variations in sound
intensity produced by 2
slightly different
frequencies
– both constructive
and destructive
interference occur

25. Interference
–The effects caused by 2 or
more waves.
•Ex. Several instruments
produce interference in
a band.

26. Cool Interference Examples:
• The Sound Barrier: the point at which the
source of a sound accelerates to the speed of
sound
• Sonic Booms: the explosive sound heard when
a shock wave reaches your ears
• 1st
time sound barrier broken: Oct. 14, 1947 by
Chuck Yeager (speed of sound is called Mach
1); so Mach 6 is going 6 times the speed of
sound

27. Sound Barrier and Sonic Booms

28. Resonance
• Forced Vibration
– when one vibrating object forces
another object to vibrate at the
same frequency
– results in a louder sound because a
greater surface area is vibrating
– used in guitars, pianos, etc.

29. Resonance
• Resonance
– special case of forced
vibration
– object is induced to vibrate
at its natural frequency

30. Harmonics
• Fundamental
– the lowest natural frequency of an object
• Overtones
– multiples of the fundamental frequency

31. • Examples
–Fundamental – 100 Hz
–1st
Overtone – 200 Hz
–2nd
Overtone – 300 Hz

32. Music vs. Noise
• Music
– specific pitches and sound quality
– regular pattern
• Noise
– no definite pitch
– no set pattern

33. Acoustics
• Acoustics
– the study of sound
• Reverberation
– echo effect produced by
the reflection of sound
Anechoic chamber - designed to
eliminate reverberation.

34. Acoustics