Transcript Chapter 16 PowerPoint

Chapter 16
Sound
Section 1 - The Nature of
Sound
• Sound - a disturbance that travels through
a medium as a longitudinal wave
– Sounds are created by vibrations.
• Drum, guitar string, vocal cords
– Sound waves carry energy through medium
(usually air)
The Nature of Sound (con’t.)
• Sound waves reflect off objects, diffract through
narrow openings and around barriers, and
interfere with others.
• Reflection – when they hit a hard surface – Echo
(harder and smoother)
• Diffraction - bending of sound waves around
barriers. Can hear around corners, or sounds
outside room with door open
• Interference – Constructive and destructive
The Nature of Sound (con’t.)
• Speed of sound
• The speed of sound depends on the elasticity,
density, and temperature of the medium the
sound travels through.
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air - 343 m/s (@ 20oC)
fresh water - 1,509 m/sec
Lead – 1,210 m/s
Aluminum – 5,000 m/s
• Elasticity - ability of a material to bounce back
after being disturbed. Very elastic material ,
particles easily go back to their original
positions, more elastic = faster.
The Nature of Sound (con’t.)
• Density- how much matter, or mass, there is in a
given amount of space or volume –
denser=Slower
• Temperature- warmer = faster
– Speed of sound in air @ 20oC – 343 m/s
– Speed of sound in air @ 0oC – 330 m/s
Section 2 - Properties of
Sound
• Loudness – describes ones perception of the
energy of a sound.
• The loudness of a sound depends on two
factors: the amount of energy it takes to make
the sound and the distance from the source of
the sound.
• Larger amplitude of vibration - increase intensity
Properties of Sound (con’t.)
• Intensity - the amount of energy the wave carries
per second through a unit area
• As one moves away from a sound source,
loudness decreases because intensity
decreases. (pg 547)
• Loudness is measured in decibels (dB)
Table pg. 548
• Each 10-dB increase in loudness represents a
tenfold increase in the intensity of the sound.
Properties of Sound (con’t.)
• Pitch - perception of the frequency of a sound –
Low frequency = low pitch
• Frequency - number of vibrations that occur per
second
– Human hearing range 20 Hz to 20,000 Hz
– Ultrasound - frequency above human range
– Infrasound - frequency below human range
• In music, a pitch is a note.
• Larynx – (voice box) You change the pitch of
your voice with your vocal cords.
Properties of Sound (con’t.)
• Doppler effect - the apparent change in
frequency as a wave source moves in relation to
the listener
• When a sound source moves, the frequency of
the waves changes because of the motion of the
source adds to the motion of the waves.
Properties of Sound (con’t.)
• Sonic boom – the release of energy when
sounds waves overlap (pg. 551)
Sonic Boom Video
Section 3 - Music
• Music - a set of notes (tones) that combine in
patterns that are pleasing
• Noise - has no pleasing timbre and no
identifiable pitch
– Interference occurs when two or more sound waves
interact.
• The sound quality of musical instruments results
from blending a fundamental tone with its
overtones. Resonance also plays a role in the
sound quality. (Timbre)
Music (con’t)
• Fundamental Tones and Overtones– A standing wave can only occur at a specific
frequencies that are called natural frequencies. Every
object has its own natural frequency. Spring demo
– Fundamental tone- The lowest natural frequency of
an object
– Overtones- The object’s higher natural frequencies
– Diagram - fundamental frequency and overtones!!!!!!!
(page 553)
Music (con’t)
• Resonance – affects the sound quality of a
musical instrument by increasing the loudness of
certain overtones.
– Ex. Opera singer shatters crystal glass
Instruments
• There are three basic groups of musical
instruments: stringed instruments, wind
instruments, and percussion instruments.
• Stringed instruments - strings vibrate, length,
thickness, material and tension of string effects
frequency. Hollow body increases loudness
through resonance.
• Wind Instruments - players lips vibrate against
mouthpiece (reed) creating a vibration. Air
column inside instrument vibrates. Length of air
column adjusted with valves or slides
determines note.
Instruments
• Percussion Instruments - instruments vibrate
when struck. Frequency effected by material
used, size of instrument and tension of drum.
Instruments (con’t.)
• Acoustics - The study of how sounds interact
with each other and the environment.
– Constructive and destructive interference
– Auditorium design
– Ear protection - destructive interference
• Reverberation – Echos of a sound are heard
after the sound source stops producing sound
waves.
Acoustics is used in the design of concert halls
to control reverberation and interference.
Instruments (con’t.)
• Beat - The regular changes in loudness of a
sound when two sounds of different frequencies
are played together. Piano tuner
Section 4 - How you hear
sound
• The outer ear funnels sound waves, the middle
ear transmits the waves inward, and the inner
ear converts the sound waves into a form that
travels to your brain.
• Ear Diagram pg. 559
• Outer ear - ear canal, eardrum
• Middle ear - hammer, anvil & stirrup
• inner ear - cochlea (cavity filled with liquid &
10,000 tiny hairs)
How You Hear Sound (con’t.)
• Hearing loss caused by injury, infection,
(birth defects,) and aging
• extended exposure to loud sounds
• Hearing aids amplify sounds and can
restore some hearing.
Section 5 – Using Sound
• Echolocation - use of reflected sound waves to
determine distances or to locate objects
• Some animals, including bats and dolphins, use
echolocation to navigate and to find food.
• Ultrasound technologies such as sonar and
ultrasound imaging are used to observe things
that cannot be seen directly.
Using Sound (Con’t.)
• Sonar - a system of detecting reflected
sound waves.
(sound navigation and ranging)
• The sonar device measures the amount of
time it takes to detect the reflected sound
waves. The longer it takes to come back,
the further away the object is. Using the
speed of sound in the medium the
distance is calculated.
Calculation example.
Using Sound (Con’t.)
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Uses of ultrasound & infrasound
dog whistle - ultrasound
dolphins & whales - echolocation
bats - echolocation
toothbrush
automatic focus camera
sonogram • ultrasound used to
look inside human
body to diagnose and
treat medical
conditions