1. Chapter 15 Sound If a tree falls in the forest and no one is there to
hear it, does it make a sound?
A sound wave is a pressure variation that is
transmitted through matter.
Sound is a longitudinal and a mechanical wave

2. Chapter 15 Sound The speed of sound in air at 0º C is 330 m/s
and increases at .6 m/s for each degree increase
in temperature.
In general, the speed of sound is faster in solids
and in liquids because the molecules are closer
together.
The frequency and the wavelength are related
by the equation v = f.

3. Chapter 15 Sound Loudness: The loudness of a sound depends
primarily on the amplitude of the pressure wave.
Loudness is measured in decibels.
Frequency: The number of cycles per second.
The human ear can detect frequencies between
20 and 20,000 Hz.
Frequency and loudness are not related.

4. Chapter 15 Sound Find the frequency and the period of a sound
wave moving in air at room temperature (20º C)
with a wavelength of .8 m.
v = f or f = v/
f = (330 m/s + (.6 m/s)(20))/.8 m
f = 342 m/s /.8 m= Hz

5. Chapter 15 Sound If a sound is made and hear the echo from a
wall 3 seconds later, how far away is the wall?
The temperature is 30º C.
d = vt
d = (330 m/s + (.6 m/s)(30) ( 1.5 s)
d = (348 m/s)(1.5 s) = 522 m

6. Chapter 15 Sound Doppler Shift: A change in sound frequency
due to the relative motion of either the source
or the detector.
Demonstration

7. Chapter 15 Sound

8. Chapter 15 Sound Resonance: When the frequency of a sound
matches the natural
frequency of an object.
Animation

9. Chapter 15 Sound

10. Chapter 15 Sound Raising and lowering the tube changes the length of
the air column. When the
air column is in resonance
with the tuning fork, the
sound is the loudest,

11. Chapter 15 Sound Musical Instruments
String -Vibration of a string resonate a sounding board.
Brass - Vibration of lips
Reed - Vibration of a column of air
Percussion - Vibration of an object, vibrates a column of
air.

12. Chapter 15 Sound Columns of /4, 3/4, 5/4, … will all be in
resonance with a tuning fork.
Demonstration

13. Chapter 15 Sound Columns of /2, , 3/2, 2, … will all be in
resonance with a tuning fork.

14. Chapter 15 Sound A tuning fork with a frequency of 392 Hz
is found to cause resonances in an air column
Spaced by 44.3 cm. The air temperature is
27º C. Find the velocity of sound in air at that
temperature.
f = 392 Hz
l = 44.3 cm
Resonances are spaced by one-half
wavelength so  = 2l
V = f = f(2l) = (392 Hz)(.866m) = 347 m/s

15. Chapter 15 Sound The frequency of a tuning fork is unknown. A
student uses an air column at 27°C and finds
resonances spaced by 39.2 cm. What is the
frequency of the tuning fork?
v = 347 m/s
l = 39.2 cm
Resonances are spaced by one-half
wavelength so  = 2l
F=v/  = 347m/s/.784 m = 443 Hz

16. Chapter 15 Sound Higher frequencies which are
Odd-number multiples of the
fundamental frequency are
called Harmonics.

17. Chapter 15 Sound
The ear consists of three basic parts -the outer ear, the middle ear, and the inner ear.Each part of the ear serves a specific purpose in the task of detecting and interpreting sound.
The outer ear serves to collect and channel sound
to the middle ear. The middle ear serves to transform
the energy of a sound wave into the internal vibrations
of the bone structure of the middle ear and ultimately
transform these vibrations into a compressional wave in
the inner ear. The inner ear serves to transform the energy
of a compressional wave within the inner ear fluid into nerve impulses which can be transmitted to the brain.

18. Chapter 15 Sound

19. Chapter 15 Sound Sound Quality Chord Several pitches played together.
Dissonance An unpleasant set of pitches.
Consonance A pleasant set of pitches.
Octave The interval between two
frequencies with a ratio of 2:1
Pythagoras noted that pleasing sounds occurred
when the strings have lengths in small
whole-number ratios, 1:2, 2:3, etc.

20. Chapter 15 Sound

21. Chapter 15 Sound

22. Chapter 15 Sound Beat Notes When two frequencies are close together
interfere to
produce high and low sounds.
Fbeat= |fa - fb|
Beats