Download Chapter 11 Section 1

Sound
• If you recall, in order to produce sound a
medium must vibrate.
• Also sound waves are a compression or
longitudinal wave. This wave is made up of
compressions and rarefactions
• Compression= when the coils of a spring a
close together
• Rarefaction= when the coils of a spring are
spread apart
wavelength, 
rarefaction
compression
• If that still confuses you then here is a molecular
break down:
– When sound travels though a medium there are
alternating regions of high and low pressure.
Compressions are high pressure areas where
molecules are packed tightly together. Rarefactions
are low pressure regions where the molecules are
more spread out.
wavelength, 
Speed of Sound
• The speed of sound depends on the substance
of the medium and it’s state of mater (solid,
liquid, or gas)
Medium
Speed of sound at room
temp (m/s, 20°
Air
347
Cork
500
Water
1,498
Brick
3,650
Aluminum
4,877
Sonic Boom
Mach Numbers and Speed
• Depending on temperature, sound travels around 374
m/s or 750 mph. This is referred to as Mach’s number or
Mach 1.
• Twice this speed or 758 m/s or 1500 mph is called Mach
2 which is about the maximum speed for the F-22 Raptor.
• Speed Racer drives a car called “The Mach 5”, which
implies it goes 5 times the speed of sound.
• The speed of sound is affected by
temperature.
• If you recall we have defined as the average
kinetic energy of particles in an object.
• The faster the particles are moving in a
medium before creating a sound allows for
faster transfer of energy from the sound wave.
Human Hearing
• Human hearing was designed to work in the slower
medium of air.
• It uses your ears to turn compressional waves into
meaning.
• It occurs in 4 stages
– First, the ear gathers the compressional waves
– Second, the ear amplifies the waves.
– Third, the amplified waves are converted into nerve
impulses
– Fourth, the nerve impulse travels to the brain where it is
then decoded and interpreted.
Sections of the ear
• Outer ear—visible part, this is where sound is
first gathered, directs it down the ear canal to
the eardrum.
• Middle ear—contains the ossicles of the ear.
– As the eardrum vibrates, then it causes vibrations
in the small bones
– The bones are the Malleus (hammer), Incus(anvil),
and the stapes (stirrup)
– The stapes vibrates the cochlea
• Inner ear—consists of the cochlea, which is
the spiral-shaped structure that is filled with
liquid and contains tiny hair cells
– When these hairs vibrate they send a signal to the
auditory nerve which takes the signal to the brain
for decoding and interpretation.
– When a person experiences hearing loss is is
usually because these hairs have become
damaged and can’t vibrate any more
Content Check
1. What are two things that affect the speed of
sound?
2. What makes an ear drum vibrate?
3. Why does sound speed up when temperature
increases?
4. Why must there be a medium for sound to exit?
5. Some people hear ringing in their ears, called
tinnitus, even in the absence of sound. Why do
you think this occurs?