Transcript Sound - MsCharboneausWiki

9.3 What is a sound wave?
• Sound waves are pressure waves with
alternating high and low pressure regions.
• When they are pushed by the vibrations, it
creates a layer of higher pressure which
results in a traveling vibration of pressure.
9.3 What is a sound wave?
• At the same temperature,
higher pressure contains
more molecules per unit of
volume than lower
pressure.
9.3 How we hear sound
• The parts of the ear work together:
1. When the eardrum
vibrates, three small
bones transmit the
vibrations to the cochlea.
2. The vibrations make
waves inside the cochlea,
which vibrates nerves in
the spiral.
3. Each part of the spiral is
sensitive to a different
frequency.
Hearing Loss & Deafness
• Tinnitus is one of the most common
types of hear loss. Results from long
term exposure to loud noises.
• The loud noise damages the hair cells
and nerve ending in the cochlea.
• Damaged hair doesn’t grow back so to
any part of the inner ear usually means
permanent hearing loss.
Protecting Your Hearing
• Loud sounds can be blocked out by
earplugs.
• Listen to things at a lower volume
• Put a distance between yourself and
the loud noises.
• When doubling the distance between
yourself and the loud sound will lessen
the sound’s intensity by ¼.
9.3 The wavelength of sound
• We usually think about
different sounds in
terms of frequency, but
wavelength is also
important.
• Musical instruments
use the wavelength of
a sound to create
different frequencies.
9.3 The wavelength of sound
• The wavelength of sound in air is similar
to the size of everyday objects.
9.3 The frequency of sound
• The pitch of a sound is
how you hear and
interpret its frequency.
• A low-frequency sound
has a low pitch.
• A high-frequency
sound has a high pitch.
Each person is saying “Hello”.
9.3 The frequency of sound
• Humans can generally hear frequencies
between 20 Hz and 20,000 Hz.
• Most sound has more than one frequency.
• Almost all the sounds you hear contain
many frequencies at the same time.
9.3 The frequency of sound
• Sounds near 2,000 Hz
seem louder than
sounds of other
frequencies, even at
the same decibel level.
• According to this
curve, a 40 dB sound
at 2,000 Hz sounds
just as loud as an 80
dB sound at 50 Hz.
9.3 The loudness of sound
• The loudness of a sound is measured in
decibels (dB).
• The decibel is a unit used to express relative
differences in the loudness of sounds.
9.3 The loudness of sound
• Most sounds fall between 0 and 100 on
the decibel scale, making it a very
convenient number to understand and use.
9.3 The Doppler effect
• When the object is moving, the frequency
will not be the same to all listeners.
• The shift in frequency caused by motion is
called the Doppler effect.
• You hear the Doppler effect when you hear
a police or fire siren coming toward you,
then going away from you.
Reflection of Sound Waves
• An echo is a reflected sound wave
• The strength of the reflected sound wave
depends on the reflecting surface
• Sound waves reflect best off of smooth, hard
surfaces
• Example: a shout in a gym will echo better
than in an auditorium because the walls in an
auditorium are designed to absorb sound,
not reflect it
Echolocation
• Reflected sound waves can be used for
many different things
• Echolocation is the process of using
reflected sound waves (echos) to find
objects
• Some animals use echos to find food, they
can tell how far away something is by how
long it takes sound waves to echo back to
their ears Examples: bats, beluga whales
• People use sonar to locate objects
underwater, helps navigators on ships avoid
icebergs, also helps to map ocean floor
Echolocation continued
• Ultrasonography is a medical
procedure that uses echos to
“see” inside a patient’s body
without doing surgery.
• Echos reflect off the patient’s
organs and are then changed into
images that can be seen on a
screen
• Used to see gallbladders,
kidneys, babies, and other
organs
Interference of Sound Waves
• Orchestras and bands make use of
constructive interference when several
instruments are playing, this causes
the combined amplitude to increase
resulting in a louder sound
9.3 The speed of sound
• Objects that move
faster than sound are
called supersonic.
• If you were on the
ground watching a
supersonic plane fly
toward you, there
would be silence.
• The sound would be
behind the plane,
racing to catch up.
9.3 The speed of sound
• A supersonic jet “squishes” the sound waves so
that a cone-shaped shock wave forms where the
waves “pile up” ahead of the plane.
• In front of the shock wave there is total silence.
• Passenger jets are subsonic because they travel
at speeds from 400 to 500 mi/hr.
Resonance
• Resonance happens when an object
vibrating at or near a resonant
frequency of a second object causes
the second object to vibrate.
• If you strike a tuning fork and hold it
near a guitar string, the guitar string
will start to vibrate