Sound waves

1. Unit 5, Chapter15
CPO Science
Foundations of Physics

2. Unit 5: Waves and Sound
 15.1 Properties of Sound
 15.2 Sound Waves
 15.3 Sound, Perception, and Music
Chapter15 Sound

3. Chapter15 Objectives
1. Explain how the pitch, loudness, and speed of sound are
related to properties of waves.
2. Describe how sound is created and recorded.
3. Give examples of refraction, diffraction, absorption, and
reflection of sound waves.
4. Explain the Dopplereffect.
5. Give a practical example of resonance with sound waves.
6. Explain the relationship between the superposition principle
and Fourier’s theorem.
7. Describe how the meaning of sound is related to frequency
and time.
8. Describe the musical scale, consonance, dissonance, and beats
in terms of sound waves.

4. Chapter15 Vocabulary Terms
 pressure
 frequency
 pitch
 superposition
principle
 decibel
 speaker
 acoustics
 microphone
 fundamental
 wavelength
 stereo
 Dopplereffect
 supersonic
frequency
 spectrum
 shockwave
 resonance
 node
 antinode
 dissonance
 harmonic
 reverberation
 note
 sonogram
 Fourier’s
theorem
 rhythm
 musical scale
 cochlea
 consonance
 longitudinal wave
 beats
 octave

5. 15.1 Properties of Sound
Key Question:
What is sound and how
do we hear it?
*Students read Section 15.1
AFTER Investigation 15.1

6. 15.1 Properties of Sound
 If you could see the
atoms, the difference
between high and low
pressure is not as great.
Here, it is exaggerated.

7. 15.2 The frequency of sound
 We hearfrequencies of sound as
having different pitch.
 A low frequency sound has a low
pitch, like the rumble of a big truck.
 A high-frequency sound has a high
pitch, like a whistle orsiren.
 In speech, women have higher
fundamental frequencies than men.

8. 15.1 Complex sound

9. Common Sounds and theirLoudness

10. 15.1 Loudness
Every increase of 20 dB,
means the pressure wave
is 10 times greaterin
amplitude.
Logarithmic
scale
Linear scale
Decibels (dB) Amplitude
0 1
20 10
40 100
60 1,000
80 10,000
100 100,000
120 1,000,000

11. 15.1 Sensitivity of the ear
 How we hearthe loudness of
sound is affected by the
frequency of the sound as well
as by the amplitude.
 The human earis most
sensitive to sounds between
300 and 3,000 Hz.
 The earis less sensitive to
sounds outside this range.
 Most of the frequencies that
make up speech are between
300 and 3,000 Hz.

12. 15.1 How sound is created
 The human voice is a complex
sound that starts in the larynx, a
small structure at the top of your
windpipe.
 The sound that starts in the larynx
is changed by passing through
openings in the throat and mouth.
 Different sounds are made by
changing both the vibrations in the
larynx and the shape of the
openings.

13. 15.1 Recording sound
1. A common way to record sound starts with a
microphone. A microphone transforms a sound wave
into an electrical signal with the same pattern of
oscillation.

14. 15.1 Recording sound
2. In modern digital recording, a sensitive circuit converts
analog sounds to digital values between 0 and 65,536.

15. 15.1 Recording sound
3. Numbers correspond to the amplitude of the signal and
are recorded as data. One second of compact-disk-
quality sound is a list of 44,100 numbers.

16. 15.1 Recording sound
4. To play the sound back, the string of numbers is read by
a laserand converted into electrical signals again by a
second circuit which reverses the process of the
previous circuit.

17. 15.1 Recording sound
5. The electrical signal is amplified until it is powerful
enough to move the coil in a speakerand reproduce the
sound.

18. 15.2 Sound Waves
Key Question:
Does sound behave like
other waves?
*Students read Section 15.2
BEFORE Investigation 15.2

19. 15.2 Sound Waves
1. Sound has both frequency (that we hear
directly) and wavelength (demonstrated by
simple experiments).
2. The speed of sound is frequency times
wavelength.
3. Resonance happens with sound.
4. Sound can be reflected, refracted, and
absorbed and also shows evidence of
interference and diffraction.

20. 15.2 Sound Waves
A sound wave is a wave of alternating high-pressure and
low-pressure regions of air.

21. 15.2 The wavelength of sound

22. 15.2 The Dopplereffect
 The shift in frequency caused by motion is called the
Dopplereffect.
 It occurs when a sound source is moving at speeds less
than the speed of sound.

24. 15.2 The speed of sound
 The speed of sound in air is 343 meters per
second (660 miles per hour) at one atmosphere
of pressure and room temperature (21°C).
 An object is subsonic when it is moving slower
than sound.

25. 15.2 The speed of sound
 We use the termsupersonic to describe motion at
speeds fasterthan the speed of sound.
 A shockwave forms where the wave fronts pile up.
 The pressure change across the shockwave is what
causes a very loud sound known as a sonic boom.

27. 15.2 Standing waves and resonance
 Spaces enclosed by boundaries can create
resonance with sound waves.
 The closed end of a pipe is a closed boundary.
 An open boundary makes an antinode in the
standing wave.
 Sounds of different frequencies are made by
standing waves.
 A particular sound is selected by designing the
length of a vibrating system to be resonant at the
desired frequency.

29. 15.2 Sound waves and boundaries
 Like other waves, sound
waves can be reflected
by surfaces and
refracted as they pass
from one material to
another.
 Sound waves reflect
from hard surfaces.
 Soft materials can
absorb sound waves.

30. 15.2 Fourier's theorem
 Fourier’s theorem says any complex wave can
be made from a sum of single frequency waves.

31. 15.2 Sound spectrum
 A complex wave is really a sumof component frequencies.
 A frequency spectrum is a graph that shows the amplitude
of each component frequency in a complex wave.

32. 15.3 Sound, Perception, and Music
Key Question:
How is musical sound
different than other
types of sound?
*Students read Section 15.3
AFTER Investigation 15.3

33. 15.3 Sound, Perception, and Music
 A single frequency by itself does not have much meaning.
 The meaning comes frompatterns in many frequencies
together.
 A sonogram is a special
kind of graph that shows
how loud sound is at
different frequencies.
 Every person’s sonogramis
different, even when saying
the same word.

34. 15.3 Hearing sound
 The eardrum vibrates in
response to sound waves
in the earcanal.
 The three delicate bones
of the innereartransmit
the vibration of the
eardrumto the side of
the cochlea.
 The fluid in the spiral of
the cochlea vibrates and
creates waves that travel
up the spiral.

35. 15.3 Sound
 The nerves nearthe
beginning see a
relatively large
channel and respond
to longerwavelength,
low frequency sound.
 The nerves at the small end of the channel respond to
shorterwavelength, higher-frequency sound.

36. 15.3 Music
 The pitch of a sound is how high orlow we hear
its frequency. Though pitch and frequency usually
mean the same thing, the way we heara pitch can
be affected by the sounds we heard before and
after.
 Rhythmis a regulartime pattern in a sound.
 Music is a combination of sound and rhythmthat
we find pleasant.
 Most of the music you listen to is created froma
pattern of frequencies called a musical scale.

38. 15.3 Consonance, dissonance, and beats
 Harmony is the study of how sounds work together to
create effects desired by the composer.
 When we hear more than one frequency of sound and
the combination sounds good, we call it consonance.
 When the combination sounds bad or unsettling, we
call it dissonance.

39. 15.3 Consonance, dissonance, and beats
 Consonance and dissonance are related to beats.
 When frequencies are far enough apart that there are
no beats, we get consonance.
 When frequencies are too close together, we hear
beats that are the cause of dissonance.
 Beats occur when two frequencies are close, but not
exactly the same.

41. 15.3 Harmonics and instruments
 The same note sounds different when played on
different instruments because the sound from an
instrument is not a single pure frequency.
 The variation comes from the harmonics, multiples of
the fundamental note.

42. Application: Sound from a Guitar