Download Sound - Ms. Lisa Cole-

Sound
Sound Wave Properties
Sound Waves are ___________________________ Waves-The air molecules shown below are
either compressed together, or spread apart. This creates alternating _____ and _____ pressure.
Frequency
•The frequency of a sound wave (or any wave) is the number of complete ___________ per
second.
•The frequency of sound determines its ________. The higher the frequency, the ______ the
pitch.
Wavelength
•Wavelength is the _________ between two high pressures, or two low pressures. This property
is dependent on the ___________ of the sound and its _____________.
•Wavelength and frequency are ________________ related.
•__________ wavelength (high frequency) results in a __________ pitch.
•http://phet.colorado.edu/simulations/sims.php?sim=Sound
Frequency and the human ear
•A young person can hear pitches with frequencies from about ____ Hz to ____________ Hz.
(most sensitive to frequencies between 1000 and 5000 Hz).
•As we grow older, our hearing range shrinks, especially at the _____ frequency end.
•By age 60, most people can hear nothing above _____________ Hz.
•Sound waves with frequencies below 20 Hz are called _____________.
•Sound waves with frequencies above 20000 Hz are called ______________.
The _____________________ of a Sound Wave Determines its loudness or softness.
The velocity of sound depends on
● the ___________ it travels through
● the ____________________ of the medium
•
•
•
•
Sound travels faster in ___________ than in air (4 times faster in water than in air)
Sound travels faster in __________ than in liquids (11 times faster in iron than in air)
Sound does not travel through a _____________ (there is no air in a vacuum so sound
has no medium to travel through)
The speed depends on the _______________ and ______________ of the medium.
Effects of Temperature
• In air at room temperature, sound travels at ____________m/s (~766 mph)
• v = 331 m/s + (0.6)T
– v: velocity of sound in air
– T: temperature of air in oC
• As temperature increases, the velocity of sound _____________
Relationship between velocity, frequency, and wavelength
V = f
V = velocity of sound
 = wavelength of sound
f = frequency of sound
Echoes are the result of the _________________ of sound. Sound waves leave a source, travel
a distance, and bounce back to the origin.
Things that use echoes...
Refraction of Sound
as the sound wave transmits into the
warmer air at lower levels, they change
direction, much like light passing
through a prism
DIFFRACTION: THE _________________ OF WAVES THROUGH A SMALL OPENING
OR AROUND AN OBSTACLE.
Doppler Effect
Sound waves move out on all directions like this:
But when they move, the ________________ of the wave gets bunched up (___________
wavelength) and the back of the wave starts to ________ (______________ wavelength):
Observer C hears a ___________ pitch (__________ frequency)
Observer B hears the ____________ pitch (no ____________ in frequency)
Observer A hears a ______ pitch (__________________ frequency)
When the source goes faster, the wave fronts in the front of the source start to bunch up closer
and closer together, until...
The object actually starts to go faster than the speed of sound. A _________________ is then
created.
•The doppler effect is a change in the ________________ frequency due to the _________ of
the source or the receiver.
•Example: As an ambulance with sirens approaches, the pitch seems _____________. As the
object moves by the pitch __________.
•http://www.grc.nasa.gov/WWW/K-12/airplane/sndwave.html
Police use the Doppler Shift when measuring your speed with radar
•A frequency is sent out of the radar gun
•The sound wave hits the speeding car
•The frequency is _______________ by the car moving away from the radar and bouncing back
•The ____________ the frequency changes determines how ________ you are going
•The ____________ you are going, the __________ the frequency is changed.
Equation that describes the doppler effect.
f = fo (v + vo)
(v - vs)
fo is the ______________ frequency being emitted
f is the ________________ frequency as the source approaches or recedes
vo is (+) if the _____________ moves _______________ the source
vo is (-) if the ____________ moves _____________ from the source
vs is (+) if the ______________ moves ______________ the observer
vs is (-) if the _____________ moves ______________ from the observer
Example
•Sitting at Six Flags one afternoon, Mark finds himself beneath the path of the airplanes leaving
Hartsfield International Airport. What frequency will Mark hear as a jet, whose engines emit
sounds at a frequency of 1000 Hz, flies toward him at a speed of 100 m/sec? (temp is 10oC)
Solution
Natural Frequency
•Nearly all objects when hit or disturbed will ________________.
•Each object vibrates at a ______________ frequency or set of frequencies.
•This frequency is called the _______________ frequency.
•If the ______________ is large enough and if the natural frequency is within the range of
___________________ Hz, then the object will produce an __________________ sound.
Timbre
•Timbre is the ________________ of the sound that is produced.
•If a ___________ frequency is produced, the tone is pure (example: a flute)
•If a ______ of frequencies is produced, but related ______________________ by wholenumber ratios, it produces a richer tone (example: a tuba)
•If ____________ frequencies are produced that are _______ related mathematically, the sound
produced is described as _______________ (example: a pencil)
Factors Affecting Natural Frequency
•______________________ of the medium
•_____________________ in the wavelength that is produced (length of string, column of air in
instrument, etc.)
•______________________ of the air
Standing Waves
 A standing wave is a wave that appears to be standing ____________.
 Standing waves result from the_________________ between the incident wave and the
reflected wave.
 As the frequency of the vibrations is increased, the number of nodes and antinodes
_________. (see figure 14-14 on page 389)
 http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave5.html
 http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave4.html
Resonance
•Resonance occurs when one object vibrates at the ______ natural frequency of a second object,
_________________ that second object into __________________________ motion.
•Example: pushing a swing
•Resonance is the cause of sound production in ______________ ____________________.
•Energy is transferred thereby ____________________ the amplitude (volume) of the sound.
Types of Resonance
•Resonance takes place in both ___________ pipe resonators and _______ pipe resonators.
•Resonance is achieved when there is a ____________ ____________ produced in the tube.
•Closed pipe resonators
–open end of tube is _________________
–closed end of tube is ____________
–http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave5.html
•Open pipe resonators
–both ends are ___________
–both ends are ___________________
•http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave4.html
Closed Pipe Resonance
Harmonics of Closed Pipe Resonance
•
•
•
The shortest column of air that can have a pressure anti-node at the closed end and a
pressure node at the open end is ____ wavelength long. This is called the fundamental
frequency or _______ harmonic.
As the frequency is increased, additional resonance lengths are found at ____ wavelength
intervals.
The frequency that corresponds to ¾ wavelength is called the ___ harmonic, 5/4
wavelength is called the _____ harmonic, etc.
Open Pipe Resonance
Harmonics of Open Pipe Resonance
• The shortest column of air that can have nodes (or antinodes) at both ends is
___wavelength long. This is called the fundamental frequency or _____ harmonic.
• As the frequency is increased, additional resonance lengths are found at ____ wavelength
intervals.
• The frequency that corresponds to a full wavelength is the ____ harmonic, 3/2
wavelength is the ____ harmonic, etc.
Problems
1. Matt is playing a toy flute, causing resonating waves in a open-end air column. The speed of
sound through the air column is 336 m/s. The length of the air column is 30.0 cm. Calculate the
frequency of the first, second, and third harmonics.
2. Tommy and the Test Tubes have a concert this weekend. The lead instrumentalist uses a test
tube (closed end air column) with a 17.2 cm air column. The speed of sound in the test tube is
340 m/s. Find the frequency of the first harmonic played by this instrument.
Sound Intensity
• The intensity of a sound is the amount of _______ transported past a given area in a unit
of time.
• Intensity = power/area
• The greater the ___________, the greater the ______ at which energy is transported-the
more ________ the sound
• Intensity is __________ related to the square of the distance. As distance _________, the
intensity __________.
Threshold of Hearing
• The human ear is sensitive to variations in ________ waves, that is, the ___________ of
sound waves.
• The ear can detect wave amplitudes of _____________ Pa up to _____ Pa.
• The amplitudes of these waves are measured on a ______________logarithmic scale
called sound level.
• Sound level is measured in ___________ (dB).
Decibel
• Measures the ______________ of sound
• Relates to the _______________ of the wave
• Every increase of 10dB has _____ greater amplitude
• Most people perceive a 10 dB increase in sound level as about ________as loud as the
original level.
Noise Pollution
 _______________ exposure to noise greater than 85-90 dB may cause hearing loss
 ________ exposures to noise sources of 100-130 dB can cause hearing loss
 A ________ exposure to a level of 140 dB or higher can cause hearing loss
Reducing Sound Intensity
• Sound proof materials weaken the pressure fluctuations either by _________ or
_____________________ the sound waves.
• When the sound waves are absorbed by soft materials, the energy is converted into
___________ energy.
Q1. A mosquito’s buzz is often rated with a decibel rating of 40 dB. Normal conversation is
often rated at 60 dB. How many times more intense is normal conversation compared to a
mosquito’s buzz?
1. 2
2. 20
3. 100
4. 200
Q2. A front row seat at a concert is given a 110 dB rating. The 15th row at the same concert is
given a rating of 100 dB. How many times more intense is the front row than the 15th row?
1. 10
2. 20
3. 100
4. 200
Q3. The average factory is given a rating of 90 dB. How many times more intense if the front
row of the concert?
1. 10
2. 20
3. 100
4. 200
Q4. Normal speech is given a rating of 60 dB. How many times more intense is the front row of
the concert?
1. 100
2. 1000
3. 10000
4. 100000
Q5. On a good night, the front row of the concert may result in a 120 dB sound level. An IPod
produces 100 dB. How many IPods would be needed to produce the same intensity level as the
front row of the concert?
1. 10
2. 20
3. 100
4. 200
Beats
A beat occurs when sound waves of two different (but very much alike) ________________ are
played next to each other. The result is _______________ and __________________
interference at regular intervals.
•
•
This ___________________ of wave amplitude is called a beat.
The frequency of a beat is the magnitude of ______________ between the frequencies of
the two waves, f= fA – fB
Q6. The G above middle C should vibrate at a frequency of 392 Hz. A piano key that
corresponds to that note vibrates at a higher frequency. When played at the same time as a G
tuning fork, a beat frequency of 2.0 Hz is heard. What is the frequency of the piano key?
1. 390 Hz
2. 392 Hz
3. 394 Hz
4. 784 Hz
Q7. An oboist hits a D with a frequency of 293.7 Hz while another plays a note with a frequency
of 291.2 Hz. What beat frequency is heard as they play at the same time?
1. 0.5
2. 1.5
3. 2.5
4. 3.5
Q8. A tuning fork produces three beats per second with a second, 392 Hz tuning fork. What is
the frequency of the first tuning fork?
1. 389
2. 392
3. 395
4. Either 1 or 3
Anatomy of the Ear
• Sound starts at the ______________
• Then goes through the _______________________________
• The sound waves will then vibrate the ___________________________ (eardrum)
which is made of a thin layer of skin.
• The tympanic membrane will then vibrate three tiny bones: the __________ (hammer),
the ___________________ (anvil), and the ________________________ (stirrup)
• The stapes will then vibrate the ______________________
• The frequency of the vibrations will stimulate particular __________ inside the cochlea
• The intensity at which these little hairs are vibrated will determine how ________ the
sound is.
• The _____________________________ will then send this signal to the brain.
Q9. The auditory canal leading to the eardrum is a closed pipe that is 3.0 cm long. What is the
lowest resonance frequency? (Uses 343 m/s for the speed of sound)
1. 290 Hz
2. 2900 Hz
3. 5800 Hz
4. 11000Hz