Transcript Sound is a wave.

Chapter 16
Sound Waves
I. Sound is a wave.
A. Sound is a type of mechanical wave.
1. produced by a vibrating object and travels through
matter
2. disturbances are vibrations-rapid back and forth
motions
3. medium vibrates in the same direction as the wave
travels and transfer energy
4. How Sound Waves Are Produced
a. started by vibrations that send out waves in all
directions
Example: vocal cords- relax when you breathe
to allow air to pass through the windpipe; they
tense up when you are about to sing or speak
5. How Sound Waves Are Detected
a. Shape of the ear (like a satellite dish) helps
collect sound waves
b. Reflected into the ear canal (tiny tube)
c. Waves strike the eardrum ( thin skin-like
membrane at the end of the ear canal) and they
vibrate.
d. Vibrations transfer from the eardrum through the
tiny bones in the middle ear (hammer, anvil and
stirrup.)
e. Vibrations reach the cochlea (30,000 hair cells)
and vibrate (bend) the tiny hairs causing the
cells to send impulses along the nerves to the
brain.
f. When your brain processes these signals, you
HEAR A SOUND!
B. Sound waves vibrate particles.
1. You cannot see the motion of waves in air.
2. Imagine striking a drum:
a. Drum skin vibrates very rapidly (pushing in
and out) and pushes against particles in the
air. Particles become bunched together
(compressions).
b. When the skin is pushed in the opposite
direction, it leaves an open space for the
particles to rush back in and fill it.
c. A listener hears all of these vibrations.
***A vacuum is empty space and has no particles so
sound cannot travel through it!
C. The speed of sound depends on its medium.
1. Sound travels more slowly than light and at different
speeds.
2. Two factors affect the speed of sound: type of
medium and the temperature
3. The Effect of the Material
a. Sound waves travel faster through liquids than in
air because liquids are denser (closely packed)
***Divers would hear a sound quicker underwater
than people above water.
b. Sound waves travel through elastic solids as well.
2. The Effect of Temperature
a. Sound travels faster through higher
temperatures (hot air).
Example: Yelling outside on a hot day very a cold
winter morning
16.1
16-2 Notes
Frequency determines pitch
• Pitch depends on freq.
• Pitch – high or low of sounds
• High Freq. = short
wavelengths = fast vibrations =
High Pitch (and vice versa)
High and Low Frequencies
• One complete wave is a cycle
• Unit of measurement (frequency & pitch)
– Hertz (Hz)
• Human Hearing Range = 20 – 20,000Hz
• Infrasound = > 20 Hz (elephants)
• Ultrasound = < 20,000 Hz (dogs, bats,
dolphins)
Natural Frequencies
• Frequency @ which object
vibrates.
• Constructive interference –
when two waves of same natural
frequency come together and add
up to create higher sound
(resonance)
Sound Quality
• Each musical instrument has special
sound quality
• Timbre (sound quality) – explained as
combination of waves.
– We hear fundamental tone.
• Overtone – higher frequency pitches
• Affected by starts & stops
Doppler Effect
• Ex. Pitch drops as ambulance
passes you
• 1. Doppler Effect – change in a
perceived pitch that occurs when
the source of receiver a sound is
moving.
Frequency & Pitch
• Sound waves that hit your ear are
closer together so pitch & freq.
are higher.
• As sound waves move away,
they still hit your ear but are
farther apart and lower in pitch.
16-3 Notes
Intensity determines
loudness
• Intensity depends on amplitude
• More energy = more intense and
louder
• Measured in decibels
• So higher amplitude = high sound
Intensity can be controlled
• Sound waves get weaker and
weaker until sound is
undetectable. (Amplitude goes
down but freq. and pitch stay
same)
• Intensity is changed by adding or
removing energy or changing
amplitude. Ex. Muffler
Amplification
• Increases strength of
electrical signal
–Ex. Adjust stereo volume
Acoustics
• Scientific study of sound
• How sound is produced or received
• How sound waves behave inside a space
– Ex. Use of acoustic tiles to absorb or redirect
waves
Damage to Hearing?
• Sensitivity of hair cells in ear make it
possible to hear but also easy to damage
those hair cells.
• Noises above 130 dB are dangerous and
140dB are very painful
16-4 Notes
Sound has many uses
• Ultrasound waves used to detect objects
– Ex. Babies
• Echolocation
– Sending out ultrasound waves and
interpreting the returning sound echoes
– Helps animals find their prey or objects in
front of them.
• Ex. Bats, Dolphins
Echolocation Bat Music Video
Sonar
• Instruments that use sound waves
(echolocation) to locate objects.
• Sound navigation & ranging.
• Send out ultrasound waves and use
the echoes to produce an image on a
screen.
–Ex. Fishing Boats, Ships
Medical Uses
• Examples: break up kidney stones,
see used to clean medical equipment,
to see inside internal organs, detect
the movement of fluids (blood flow)
through the body, checking the health
of a fetus during pregnancy
Sound Waves and MUSIC!!
• Create clear pitches or rhythms.
• Vibrate @ natural frequencies.
• Some have diff. parts that vibrate to
make diff. pitches.
• Stringed, wind, and percussion – 3
main types. **(electronic = 4th type)
Sound can be recorded and
reproduced
• Long distance voice communication
• Translates then reproduces sound
–Ex. Telephone
• Recorded sound
–Occurs in real time
–Sound waves turned into electrical
signals