Transcript Chapter 21 Sound

Chapter 21 Sound
What is Sound
• All sounds are produced by something that vibrates
• A wave carries energy from one place to another and
without transferring matter
• The vibrating object causes air molecules to move back
and forth
• As these air molecules collide with those nearby , they
cause other molecules to move back and forth
• A sound wave is a compressional wave, like a wave
moving through a coiled spring
• In sound waves, air molecules move back and forth
along the direction of the wave
Making Sound Waves
• When an object vibrates, it exerts a force on the
surrounding air
• For example, as the end of the tuning fork moves
outward into the air, it pushes the air molecules together
• As a result, a region where the air molecules are closer
together, or more dense, is created
• This region of high density is called a compression
• When the tuning fork moves back it causes an area of
low density called rarefaction
• The compression and rarefaction move away from the
tuning fork as molecules collide with one another
• Sound waves can be described by its
wavelengths and frequency
• Wavelength is the distance between two
consecutive compressions or two consecutive
rarefaction
• Frequency of a sound is the number of
compressions or rarefactions that pass by a
given point in one second
• The unit of frequency is the number of
wavelengths per second, or Hertz (Hz)
Speed of Sound
• Speed of sound varies because of temperature and
material it is passing through
– Sound moves faster in solid then liquids or gases because the
particles that makes solid up are closer together
– Sound is slowest in gases because molecules are farther apart
– As the temperature heats up its molecules move faster, so they
collide more frequently
• More frequent the collision the faster sound travels
• 0* C sound travels a 331m/s, 20*C 343m/s
Amplitude and Loudness
• Loudness is the human perception of how
much energy a sound wave is carrying
• The amount of energy a wave carries
depends on its amplitude
– Higher amplitude- more compressed the
particles in a compression are and the farther
they are spread out in a rarefaction
– Higher amplitude means more energy and
louder
Decibel Scale
• Scale used to describe sound waves
• Increase in 10 decibels means that the energy carried by the wave
has increased 10 times
• Increase in 20 decibels, energy increases 100 times
• Increase in 30 decibels, energy incresed 1000x
• Hearing Damage begins to occur at 85 dB
• Jet Plane = 150 dB
• Whisper =15dB
• Lawn Mower =110
Frequency and Pitch
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Pitch of a sound is how high or low it sounds
Pitch corresponds with frequency of the sound
High the pitch the higher the frequency
Lower the pitch the lower the frequency
Human ear can detect sound waves with frequencies between about 20Hz
and 20,000Hz.
Dogs can hear frequencies up to almost 50,000 Hz
Dolphins and Bats can hear frequencies as high as 150,000 Hz.
Higher pitch - shorter wavelengths, Lower pitch – Longer Wavelength
Length and thickness of your vocal cords help determine your pitch
Short thinner vocal cords vibrate at higher frequencies, results in higher
voices
Muscles in throat can stretch the vocal cords tighter, letting people vary their
pitch
Wavelength, Frequency, and Pitch
posterior lateral
Echoes
• A echoes is a reflected sound wave
• Sound waves reflect off of hard surfaces
• Sonar systems use sound waves to map out objects underwater
– The amount of time it takes for echoes to return depends on how
far away the reflecting surface is
• Echolocation – the ability to emit high pitched squeaks and listen for
echoes. Used to navigate and hunt
• Bats and dolphins use echolocation
Dolphins produce high frequency clicks that pass
through the melon. These sound waves bounce off
objects in the water and return to the dolphin in the
form of an echo
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Doppler Effect
• The change in a frequency that occurs when the source of the
sound is moving relative to a listener is the Doppler effect
• Occurs whether the sound source or the listener is moving
• As you move closer to the source you encounter each sound wave a
little earlier
– The closer you get the higher the pitch
• When you move away , each sound wave takes longer to reach you,
you hear fewer wavelength, which results in a lower pitch
• Radar guns used to determine speed of cars and baseballs use the
Doppler Effect
Diffraction
• Diffraction means that sound waves can bend around
obstacles or spread out after passing through a narrow
opening
• The amount of diffraction depends on the wavelength
• If Wavelength is much smaller than the obstacle, almost
diffraction occurs
• If wavelength is closer or larger then the size of the
obstacle, the amount of diffraction increases
Using Sound Waves
• Ultrasound – using high frequency sound
waves as an alternative to some surgeries
– Kidney stones and gall stone sometimes can
be broken up using ultrasound
– Used to exam a developing fetus, and internal
organs
The Ear
• The ear is a complex organ that is able to
detect a wide range of sounds
• Has three parts
– Outer Ear
– Middle Ear
– Inner Ear
• The Outer Ear
– Collects sound waves and directs them into
the ear canal
– Shaped like a funnel to collect sound waves
– Animals that rely on hearing to locate
predators or pry often have large ears and
can be adjusted
• Rabbits and Owls
Ural Owl Ear
• The Middle Ear
– Sound waves vibrate the Eardrum
– Eardrum is a Thin membrane that stretches
across the ear canal
– As the eardrum vibrates, it transmits
vibrations to three small bones
• Hammer
• Anvil
• Stirrup
• The bones amplify (intensify) the
vibrations
• Similar to how a lever can change a small
movement at one end into a large
movement at the other end
• Ruptured Eardrum
• Inner Ear
– The stirrup vibrates a second membrane
called the oral window
– Inner ear is filled with fluid
– Vibrations are transferred to hair tipped cells
in the cochlea
– Different sounds vibrate the hairs differently
– Cells generate signals containing information
about the frequency, intensity, and duration of
the sound
• The nerve impulse travels to the brain
along the auditory nerve
How does your ear work ?
Watch the video (Real Player needed)
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Hearing Loss
• The ear can be
damaged by disease,
age, and exposure to
loud sounds
• Constant exposure to
loud sounds can
damage the hair cells
in the cochlea
• If hair cells die, hearing loss occurs because
mammals can not produce new hair cells
• Higher frequency hearing is usually the first to
be lost
• Soft consonants sounds such as s, f, h, sh, ch
are hard to hear
• People with high frequency hearing loss have
trouble distinguishing these sound during
conversation