Sound

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Sound
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Sound
Sound a longitudinal wave phenomena that
consists of successive compressions and
rarefactions of the medium through which it
travels
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Sound
All sounds are waves produced by the vibrations
of material objects. Sound waves must have an
elastic medium in which to travel.
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compression
rarefaction
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How do you hear?
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Sonic Spectrum
so what can we hear?

• Our ears are only sensitive to a certain range of
  sound wave frequencies. This range is between
  20Hz and 20,000 Hz.
• Infrasonic below 20 HzElephants
• Ultrasonic - above 20,000 Hz.dogs

NCH Tone Generator http//www.world-voices.com/sof
tware/nchtone.html
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Pitch and Frequency

• Pitch refers to whether a sound is low or high

• It is the frequency of the wave that determines
  its pitch. A sound wave whose frequency is low
  sounds low in pitch, and vice versa.

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Intensity

• The intensity of a sound refers to the amount of
  energy (amplitude) the sound wave is carrying.

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Relative Intensity

• The comparison of the intensity of a sound to
• the intensity at the threshold of hearing.
• The Decibel Scale

ß decibels, db 10 log (I/lo) I current
Intensity lo 10-12 watts/m2 (threshold of
hearing)
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Since the scale is a 10 log scale, for every 10
decibel increase in intensity, the energy
increases 10 times.
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Loudness
A sensation in the human consciousness. It
depends on the listener and can be related to the
intensity of sound.
also known as Volume
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How is loudness and intensity related?
For every 10 decibel increase in intensity, the
loudness is doubled!
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Intensity 102 100x Loudness 22 4x
Intensity 10x Loudness 2x
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When the decibel level of traffic in the street
goes from 40 to 60 db, how much louder does the
traffic noise seem? how much more intense is the
traffic noise?
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A noisy machine in a factory produces a decibel
rating of 80 db. How many identical machines
could you add to the factory without exceeding
the 90 dB limit set by federal guidelines?
Answer 9 machines (for a total of ten)
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What is the difference between these two sounds?
What about these two sounds?
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Pitch and Intensity
1. Loud low pitched 2. Soft high pitched 3.
Med-loud high pitched
4. Loud high pitched 5. Soft low pitched 6.
Medium pitch loud
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http//www.youtube.com/watch?vY5KaeCZ_AaY The
Big Bang TheoryDoppler Effect Definition
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Frequency and Speed of a Wave
While frequency refers to the number of
vibrations which an individual particle makes per
unit of time, speed refers to the distance which
the disturbance travels per unit of time.
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The speed of a sound wave depends upon how well
the medium transfers the energy from particle to
particle.
In general, solids have the strongest
interactions between particles, followed by
liquids and then gases. For this reason,
longitudinal sound waves travel faster in solids
than they do in liquids than they do in gases.
vsolids gt vliquids gt vgases
http//www.youtube.com/watch?v5Ip4Sa5ZtBQfeature
PlayListp8DC00582647B1030playnext1playnext_f
romPLindex5 MYTHBUSTERS
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Sound waves of all frequencies have the same
speed as they move through the air.
SPEED OF SOUND
The speed of sound depends on the average speed
of the air molecules.
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Speed of Sound and Refraction
Sound travels faster in warm air. Why?
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Speed of Sound and Refraction
Sound travels faster in warm air. Why?
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So at higher temperatures the speed of sound is
faster because of the faster moving molecules. At
0 degrees the speed in air is 331.5 m/s. This
speed increases with the temperature at about 0.6
m/s per degree Celsius.

• Speed of sound (331.5 0.6T) m/s
• where T temperature in Celsius

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Sample Problem 1 Speed of Sound
Late one summer night ( T 20 degrees Celsius),
lightening is seen from an approaching storm and
five seconds later, thunder sound is heard. How
far away is the storm?

• Speed of sound ((331.5) 0.6(20))m/s
• Speed of sound 343.5 m/s
• v d/t
• 343.5 m/s d / 5s
• d 1717.5 m

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An oceanic depth-sounding vessel surveys the
ocean bottom with ultrasonic sound that travels
1530 m/s in seawater. How deep is the water if
the time delay of the echo from the ocean floor
is 2 seconds?
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I drop a stone, from rest, down a mine shaft
200 m deep. a. Find the time to hit the bottom.
(time from his hand to the bottom of shaft.
Remember, a -9.8 m/s2, use constant
acceleration equations.freefall equations) b.
Find the time to hear an echo. (time for sound to
travel from bottom of the shaft to his ear) c.
Find the total time it takes for me to hear the
stone hit the bottom of the shaft. (time from
hand to hearing the sound of the echo) T 20 oC
a) 6.39 s b) .58 s c) 6.97 s
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Water Bug
These are ripple waves made by a water bug on the
surface of the water. For each of the wave
patterns below we can see that the bug has been
moving
a. Continuously to the left b. Continuously to
the right c. Back and forth d. In a circle e.
Not at all
Water bug sample
http//www.lon-capa.org/mmp/applist/doppler/d.htm
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Doppler Effect apparent change in frequency of a
wave caused by the relative motion between the
source and the observer
http//www.colorado.edu/physics/2000/applets/doppl
er.html
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http//www.youtube.com/watch?vJ43lAESftPsfeature
related The Big Bang Theory Doppler Effect
Example
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http//www.lon-capa.org/mmp/applist/doppler/d.htm

• If the object is outrunning the waves it
  produces, the wave crests overlap one another and
  form a single crest of very large amplitude
  (interference).

• The familiar bow wave generated by a speeding
  boat knifing through the water is actually the
  superposition of many circular waves.

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Sonic Boom
When an airplane outruns its sound waves a
shock wave is formed. When the shock wave passes
a listener, a very loud sonic boom is heard.
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Sonic Boom
F14 sample
Sonic boom sound
Multiple examples
http//www.youtube.com/watch?v-d9A2oq1N38
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Sonic Boom
Shock wave

• Requirements
• vairplane gt vsound
• Based on Doppler Effect
• Shock wave occurs b/c
• Constructive Interference waves overlap

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Beats
The interference of two sound waves having
different frequencies produces beats.
http//library.thinkquest.org/19537/java/Beats.htm
l
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Beats are the periodic variation of the loudness
of sound due to constructive and destructive
interference between the waves.
Where is the sound the loudest?
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Interference of Point Sources
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Interference
. On the diagram below there are 2 point sources
where the dark lines are the crests. Identify
the type of interference, whether it is a node or
anti-node, and what phase it is in (trough, crest
or in between phase)
Pt. 1
Pt. 2
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Pitch/Decibel Quiz

• a) Pitch is related to what physical
  characteristic of a wave?
• b) Loudness?
• A sound increases in decibel level from 20 dB to
  60 dB. Relate the increase in intensity to the
  increase in loudness.
• Explain in detail what causes beats.
• How is a sonic boom formed?

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Meeky Mouse
Meeky Mouse wants to get the ball bearing up and
out of the bowl, but the ball is too heavy and
the sides of the bowl are too steep for Meeky
Mouse to support the bearings weight. Using
only its own strength without the help of levers
and such, Meeky a. Cant get the
ball bearing up and out b. Can get the ball
bearing up and out (but how??)
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Resonance

• When the frequency of forced vibrations on a
  object matches the objects natural frequency, a
  dramatic increase in amplitude occurs.
  This is called resonance.

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Standing Waves
STANDING WAVES occur in any material with
definite boundaries, as a result of superposition
of original and reflected waves within the
material
The waves must have the same amplitude and
wavelength traveling in opposite directions In a
standing wave, the particles of the wave at the
nodes are stationary.
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Terms for Sound Test

• Characteristics of a Sound Wave
• Mechanical (need source and medium)
• Longitudinal (Compressions and Rarefactions)
• Frequency and Pitch
• Amplitude and Loudness
• Decibel Sound Level Scale
• Difference between loudness and intensity
• Speed of a Sound Wave
• Determined by the medium
• Air temperature changes the speed
• vs 331.5 m/s 6T(C)
• Refraction of Sound
• Doppler Effect
• Sonic Boom

• Interference of Sound Waves
• Constructive and Destructive Interference
• Beats
• Two Point Sources
• Resonance
• Standing Wave Patterns
• Musical Instruments
• Harmonics
• Vibrating Strings
• Vibrating Air Columns
• Open-Ended
• Closed-Ended
• Quality of Music