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A Closer Look

Hearing Problems

hree general areas of hearing problems short eustachian tubes that can become loud sounds. Loud concerts, loud ear buds,
Tare related to your age and the intensity swollen from a cold, and this traps fluid in and riding in a “boom car” are examples of
and duration of sounds falling on your ears. the middle ear. Fluid buildup causes pain situations that will speed the loss of ability to
These are (1) middle ear infections of young and discomfort, as well as reduced hearing hear higher frequencies. A boom car is one
children; (2) loss of ability to hear higher fre- ability. This condition often clears on its with loud music you can hear “booming” a
quencies because of aging; and (3) ringing and own in several weeks or more. For severe half a block or more away.
other types of noise heard in the head or ear. and recurring cases, small tubes are some- Tinnitus is a sensation of sound, as a
Middle ear infections are one of the times inserted through the eardrum to ringing or swishing, that seems to originate in
most common illnesses of young children. allow fluid drainage. These tubes eventually the ears or head and can only be heard by the
The middle ear is a small chamber behind fall out, and the eardrum heals. person affected. There are a number of dif-
the eardrum that has three tiny bones that A normal loss of hearing occurs because ferent causes, but the most common is nerve
transfer sound vibrations from the eardrum of aging. This loss is more pronounced for damage in the inner ear. Exposure to loud
to the inner ear (see Figure 5.11). The mid- higher frequencies and is also greater in noises, explosions, firearms, and loud bands
dle ear is connected to the throat by a small males than females. The normal loss of hear- are common causes of tinnitus. Advancing
tube named the eustachian tube. This tube ing begins in the early twenties and then age and certain medications, such as aspirin,
allows air pressure to be balanced behind increases through the sixties and seven- can also cause tinnitus. Stopping the medi-
the eardrum. A middle ear infection usu- ties. However, this process is accelerated by cations can end the tinnitus, but there is no
ally begins with a cold. Small children have spending a lot of time in places with very treatment for nerve damage to the inner ear.

TABLE 5.1 The air temperature influences how rapidly sound
moves through the air. The gas molecules in warmer air
Speed of sound in various materials have a greater kinetic energy than those of cooler air. The
Medium m/s ft/s molecules of warmer air therefore transmit an impulse from
molecule to molecule more rapidly. More precisely, the speed
Carbon dioxide (0°C) 259 850
of a sound wave increases 0.600 m/s (2.00 ft/s) for each Cel-
Dry air (0°C) 331 1,087 sius degree increase in temperature above 0°C. So, it will be
Helium (0°C) 965 3,166 easier for your car or airplane to break the sound barrier on
Hydrogen (0°C) 1,284 4,213 a cold day than on a warm day. How much easier? In dry air
Water (25°C) 1,497 4,911 at sea-level density (normal pressure) at 0°C, the speed of
Seawater (25°C) 1,530 5,023 sound is about 331 m/s (1,087 ft/s). If the air temperature
Lead 1,960 6,430 is 30°C, sound will travel 0.600 m/s faster for each degree
above 0°C, or (0.600 m/s per 0°C)(30°C) = 18 m/s. Adding
Glass 5,100 16,732
this to the speed of sound at 0°C, you have 331 m/s + 18 m/s =
Steel 5,940 19,488
349 m/s. You would need to move at 349 m/s to travel at the
speed of sound when the air temperature is 30°C, but you

Thus, there is a reason for the old saying “Keep your ear to the could also travel at the speed of sound at 331 m/s when the
ground,” because sounds move through solids more rapidly air temperature is 0°C.

than through a gas (Table 5.1). The simple relationship of the speed of sound at 0°C plus
the fractional increase per degree above 0°C can be combined
VELOCITY OF SOUND IN AIR as in the following equations:
Most people have observed that sound takes some period of _
)
(
0.600 m∙s

(m/s) = v 0 + T p )
(
time to move through the air. If you watch a person hammering °C
v T p
on a roof a block away, the sounds of the hammering are not
equation 5.4
in sync with what you see. Light travels so rapidly that you can
consider what you see to be simultaneous with what is actually where v Tp is the velocity of sound at the present temperature, v 0
happening for all practical purposes. Sound, however, travels is the velocity of sound at 0°C, and T p is the present temperature.
much more slowly, and the sounds arrive late in comparison to This equation tells you that the velocity of a sound wave increases

what you are seeing. This is dramatically illustrated by seeing a 0.6 m/s for each degree C above 0°C. For units of ft /s,
flash of lightning, then hearing thunder seconds later. Perhaps _

)
2.00 ft∙s
(

(
you know of a way to estimate the distance to a lightning fl ash v T p (ft/s) = v 0 + °C T p )
by timing the interval between the flash and boom. If not, you

will learn a precise way to measure this distance shortly. equation 5.5
5-9 CHAPTER 5 Wave Motions and Sound 123