# Sound Notes Physcial Science 2012x

Urban and Civil

Nov 29, 2013 (4 years and 5 months ago)

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A FEW “NOTES” on SOUND...

Describe what factors affect the speed of sound

General

Information
:

Sound

is a ______________________ wave produced by a __________________ that
causes a change in ____________________. The sound wave circles out from the
source.

The wave produces high and low
pressure

regions.
Sound can be
represented by a sine curve that
shows how the pressure changes
over time.

The high pressure regions are called _______________________,

The low pressure regions are called

__________________________.

Wave Characteristics
:

Wavelength

is measured by the distance from
______
_________________________________________________________________

Amplitude

is me
asured by __________________________________________

The
speed

of sound ____________________ with increasing
temperature!

Why?

v
sound

=

Practice Examples:

a.

What is

the speed of sound in 0° C?

b.

What is the speed of sound in 20° C?

Note: The equations for WAVES that we have learned apply to sound waves as well!

Interesting Facts
:

Sound

is a mechanical wave that

must travel through a ______________________.

o

Examples

of different media
:

d
v
t

v f

 

Sound CANNOT travel through a _____________________!

o

Note: This is a HUGE error mad
e in science fiction
movies...

Sound waves travel in
solids,

liquids and gases.

o

S
ound travels slowest in ___________
____
and fastest in ______________
(11 times faster in steel!).

o

Why?

Pitch of a note
:

Pitch

is determined by ____________________________.

o

High Frequency = _________ Pitch

Examples:

o

Low
Frequency = _________ Pitch

Examples:

Only a small range of frequencies are
audible
:
we can hear from about 20 Hz

20,000
Hz
depending on age!

We can’t hear:

o

Ultrasonic Waves
: above 20,000 Hz

o

Infrasonic Waves
: below 20 Hz

Loudness and Intensity of a Sound
:

Loudness

(volume)

depends on __________________.

o

Larger amplitude means louder sound!

Intensity

of Sound
:
The amount of energy which is
transported past a given area of the medium per unit of time
.

Inverse Square Law
:
The intensity of a sound wave decreases as the distance

increases
.

o

The sound is ______ as intense at point B and _____as intense at poin
t
C as it is at point
A.

Frequency

Who Can Hear It

8000 Hz

Everyone

10,000 Hz

60 and younger

12,000 Hz

50 and younger

14,100 Hz

49 and younger

14,900 Hz

39 and younger

15,800 Hz

30 and younger

16,700 Hz

Less than 24 years old

17,700 Hz

Less than 24 years old

18,800 Hz

Less than 24 years old

19,800 Hz

Less than 24 years old

21,100 Hz

Less than 24 years old

24,000 Hz

Less than 24 years old

REFLECTION, REFRACTION, DIFFRACTION, and INTERFERENCE

of SOUND!!!

REFLECTION
:

• When

a wave reaches the boundary between two media, a portion of the
wave undergoes reflection and a portion of the wave undergoes transmission
across the boundary.

• Depending on the surface it hits, reflection of sound can lead to an
_____

(in
a large space
where the sound reflects more than 0.1 s later) or a
_________

(in a
small area/room
where the sound reflects

back to yo
ur ear in less than 0.1
second)
.

Example:

Whispering Gallery

REFRACTION
:

• When a wave passes from one medium to another, it can cha
nge speed and
wavelength (and possibly direction).

• Refraction of sound waves is most evident in situations in which the sound
wave passes through a medium with gradually varying properties.

Example:

_________________________

DIFFRACTION:

Waves BEND as they pass through an opening or around a barrier in their
path.

• Sound waves diffract around
__________

or through
____________
, allowing us
to hear others who are speaking to us from adjacent rooms.

Example:

At a parade you hear the low frequency instruments of the
marching band (bass drum, etc.) from around the first because of their
long wavelength and therefore ability to diffract more efficiently.

INTERFERENCE:

• Constructive:

Compression

+
Compr
ession

=

____ SOUND!

(high pressure)

(high pressure)

• Destructive:

Compression

+
Rarefaction

=

____

SOUND!

(high pressure)

(
low

pressure)

Beats

are heard when two sound waves of very similar frequencies interfere.
The volume oscillates from high to low intensity at the
______________
found by
finding the difference in frequency between the two notes
.

f
b
e
a
t

f
1

f
2