Transcript Chapter 2: Sound


If a tree falls in the forest and there’s no one
around to hear it, does it make a sound?

Sound
◦ A disturbance that travels through a medium as a
longitudinal wave.
◦ Sound begins as a vibration.
◦ These vibrations disturb nearby air particles.
 Every time the something vibrates outward it creates a
compression by pushing air particles together.
 When that same object vibrates in the opposite
direction the air particles bounce back and spread out
causing a rarefaction.

Sound is a mechanical wave.
◦ So sound has to move through a medium.
◦ Most often this is air, a gas, but it can also move
through solids, and liquids.
◦ Each particle of the medium vibrates one after
another in a long chain reaction.
◦ This happens until the sound waves hit your ear, at
which point you hear the sound.
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Pg. 35
◦ Vocabulary
◦ Figure 1

Pg. 36
◦ Assess your understanding
◦ Got it?

What is sound? Why can we call sound a
mechanical wave?

Sound travels much slower than light does.
◦ You will almost always see an action or light before
you hear a sound.
◦ Depending on the medium it travels through the
speed of sound can change.

Temperature
◦ The speed of sound depends on the temperature of
the medium it travels through.
◦ Sound travels slower in low temperatures and faster
in high temperatures.

Stiffness
◦ The speed of sound depends on the stiffness of the
medium it travels through.
◦ Sounds travel quicker through a stiff medium
because the particles of the medium are very close
together.
◦ Sound travels fastest in solids, second fastest in
liquids, and slowest in gases.

Density
◦ The speed of sound depends on the density of the
medium it travels through.
◦ If two media are the same stiffness, sound will
travel faster in the less dense material, and slower
in the denser material.
◦ Density is how much matter or mass there is in a
given amount of space or volume.
◦ It is much harder for particles to vibrate in dense
material, making sound slower.

Pg. 39
◦ Figure 4
◦ Assess your understanding
◦ Got It?

Why do temperature, stiffness, and density
affect the speed of sound?

Pitch
◦ A description of how high or low the sound seems
to a person.
◦ The pitch you hear depends on the frequency of the
sound wave.
◦ High pitch=High frequency
◦ Low pitch=Low frequency

Recall that frequency is how fast the wave, in
this case sound is vibrating.
◦ Air moving past your vocal cords causes them to
vibrate. The faster they vibrate the higher the
frequency.

Recall that frequency is measured in Hertz
(Hz).
◦ This is the number of waves in a second.
◦ The greater the number of hertz, the more waves
go by in a second.
◦ People, especially younger people can hear in a
range of 20 Hz to 20,000 Hz.
◦ Mice can hear in the greatest range, 1,000 Hz to
91,000 Hz.

Pg. 41
◦ Figure 1
◦ Got It?

Loudness
◦ Describes the awareness of the energy of a sound.
◦ The closer you are to a sound the louder it is.
◦ It also depends on the energy and intensity of the
sound wave.

Energy
◦ The more energy a sound has the louder it will be.
◦ The more energy the sound has the greater the
amplitude.

Intensity
◦ The amount of energy a sound wave carries per
second through a specific area.
 The greater the intensity the louder the sound.
◦ Sound spreads out as it gets farther away from the
source.
 But the total amount of energy never changes.
◦ The closer you are to the source of the sound the
closer the sound waves are together.
 This makes the sound seem louder if you are closer to
it.

What two factors affect the loudness of a
sound?

Measuring Loudness
◦ Decibel (dB)
 A unit for comparing the loudness of different sounds.
◦ A sound you can barely hear is about 0 dB.
◦ While a sound greater than 100 dB can cause
damage to your ears.
 Especially if you were to listen to that sound for a long
time.
 This is why many people such as musicians, airport
workers, and construction workers will use some sort
of hearing protection.

Examples:
◦ A sound that is 10 dB is ten times louder than a
sound that is 0 dB.
◦ A sound that is 100 dB is one hundred times louder
than a sound that is 0 dB.
 That same sound is ten times louder than a sound that
is 10 dB.
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Pg. 42
◦ Figure 2
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Pg. 43
◦ Apply It!
 #1-4
◦ Assess your understanding
 #1a-c
◦ Got it?

Doppler Effect
◦ The change in frequency of a wave as its source
moves in relation to an observer.
◦ As the sound move towards you and away from you
the frequency changes.
◦ With sound waves this is heard as a change in pitch.
◦ The motion of the wave causes the waves to either
get closer together or spread out.
◦ This principle is named for Christian Doppler an
Austrian scientist.

Doppler Effect (cont.)
◦ Waves that are closer together have a shorter
wavelength but a higher frequency.
◦ Waves that are farther apart have a longer
wavelength and a lower frequency.
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Pg. 44
◦ Compare and Contrast
◦ Figure 3
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Pg. 45
◦ Compare and Contrast
◦ Assess your understanding
◦ Got it?

What is music? How is music different from
sound or noise?

Music
◦ A set of notes that combine in patterns that are
pleasing.
◦ Noise, on the other hand does not usually have
pleasing patterns.

When you describe a sound as pleasant or
unpleasant you are describing sound quality.
◦ The sound quality of music depends on the
instruments making music and how they blend
together.

Standing waves occur when all musical
instruments are played.
◦ Recall that standing waves can only happen at
natural frequencies.

Fundamental Tone
◦ The lowest natural frequency.

Overtones
◦ Higher natural frequencies that are two, three, or
more times the frequency of the fundamental tone.

Most instruments produce several natural
frequencies at once.
◦ The fundamental tone determines which note you
hear.
◦ Each instrument produces different overtones, so
the blending of the fundamental tones and
overtones produces different sound qualities.
◦ Size, shape, and what the instrument is made of all
determine which overtones are loudest.

Pg. 47
◦ Apply It!

What determines which instruments are the
loudest?

Groups of Musical Instruments
◦ To control pitch the musician must change the
fundamental tones.
◦ To control loudness the musician changes the
energy of the vibrations.
◦ Depending on the instrument group pitch and
loudness are controlled in different ways.

String Instruments
◦ Includes guitars, pianos, violins, cellos, etc.
◦ These instruments produce sound when their
strings vibrate.
◦ Pitch is controlled by the length of the string.
 As well as the material, thickness, and tightness.
◦ Loudness is controlled by the energy applied to the
string.

Percussion Instruments
◦ Includes drums, bells, xylophone, and cymbals.
◦ These instruments produce sound when they are
struck.
◦ Pitch depends on the material they are made of, the
size of the instrument, and which part of the
instrument is played.
◦ Loudness is controlled by the amount of energy
transferred into the instrument.
 To increase the loudness the musician strikes the
instrument harder.

Wind Instruments
◦ Includes the flute, trumpet, saxophone, and many
others.
◦ These instruments produce sound when air vibrates
on or across the mouthpiece.
 This causes the air within the instrument to vibrate.
◦ Pitch is changed by changing the length of the air
column in the instrument.
 The length of the air column is controlled by keys and
valves, and other parts of the instrument.
◦ Loudness is controlled by how hard the musician
blows into the instrument.
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Pg. 48
◦ Figure 1
◦ Figure 2
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Pg. 49
◦ Figure 3
◦ Assess Your Understanding
◦ Got It?

What are the three different categories of
instruments? What instruments might not fit
in these categories?

Echo
◦ A reflected sound wave.
◦ The sound wave hits a surface and can’t pass
through it.
 In the case of an echo it reflects off.
◦ Understanding sound and echoes has allowed
scientists to make many useful pieces of tecnology.

Echolocation
◦ The use of reflected sound waves to determine
distances or to locate objects.
◦ This allows different species of animal to move
around easily in the dark.
◦ Dolphins and bats use this technique for navigating
and finding food.
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Ultrasound
◦ Sound waves with frequencies above the normal
human range of hearing.

Ultrasound (cont.)
◦ Ultra means beyond or above, so in this case it
means beyond or above sound, or hearing.
◦ Bats use ultrasound waves to hunt and navigate.
 They send out short pulses of ultrasound waves which
reflect off of objects and return to the bat’s ears.
 The time it takes for the sound to return tells the bat
how far it is away from an obstacle or prey.
 Dolphins use ultrasound in similar ways, except it
travels through water instead of air, and they sense the
reflected waves through their jawbones.
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Pg. 55
◦ Figure 1

Ultrasound Technologies
◦ Humans do not have the ability to send out
ultrasound pulses.
◦ However scientists have created technology that
uses ultrasound to our advantage.

Sonar
◦ A system that uses reflected sound waves to detect
and locate objects under water.
◦ It is used to determine the depth of water, map the
ocean floor, and locate objects or organisms.

Pg. 56
◦ Apply It!

Ultrasound Imaging
◦ Using ultrasound waves doctors are able to see
inside the human body.
◦ Different parts of the body all sound differently
when the sound reflects off of them.

Sonogram
◦ A picture created by the reflecting sound waves.
◦ Sonograms can be used to diagnose and treat
disease.
 As well as see a developing baby.
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Pg. 57
◦ Figure 2
◦ Assess your understanding.
◦ Got It?

Pg. 59-60
◦ Ch. 2 Review
◦ #1-14
◦ #18-20