Waves and Sound

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Waves and Sound

• Chapter 17

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Characteristics of Waves
Waves A rhythmic disturbance that carries energy.
Medium A material through which waves transfer.
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Mechanical Waves

• A mechanical wave is created when a source of
  energy causes a vibration to travel through a
  medium.

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Transverse Wave
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Transverse Wave
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Transverse Wave
A wave in which the medium moves at a right angle
to the direction the wave is traveling.
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Crest The top of the wave.
Trough The bottom or valley of the wave.
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Longitudinal Waves
Matter vibrates in the same direction as the
wave travels.
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Longitudinal Waves
Rarefaction
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Surface Wave
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Surface Wave
A wave that travels along a surface separating
two media.
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Homework
Section 17.1Due 4/28/09
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Amplitude The greatest distance the particles in
a wave rise or fall from their rest position. The
energy of the wave depends on the amplitude.
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Wavelength(?- lambda, m) The distance between a
point on one wave and the same identical point on
the next wave.
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Wave Velocity(v, m/s) The distance traveled by
any point on the wave in one second.
Wave Velocity depends on the medium the wave is
traveling in.
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Frequency(f, Hz) The number of waves that pass a
point in a second.
Hertz(Hz) The unit used to measure frequency.
One Hz is equal to one wave per second.
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Period (T, s) How fast one wave passes a point.
Measured in seconds.
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Relationship between Frequency and Period
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velocity wavelength X frequency
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Wheel of Answers
? x f
v
v
?
?
f
f
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Example 1 A tuning fork has a frequency of 256
hertz. The wavelength of the sound produced by
the fork is 1.32 meters. Calculate the velocity
of the wave.
Given ? 1.32m Find v f
256Hz
Basic Equation v ? X f
Solve v ? X f (1.32m) X (256Hz)
v 338m/s
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Example 2 A wave has a wavelength of 1.20
meters. Its velocity is 0.75 meters per second.
What is the frequency of the wave.
Given ? 1.20m Find f v 0.75m/s
Basic Equation f v/?
Solve f (0.75m/s) (1.20m)
f 0.63Hz
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Homework
Practice Problems 9-10Page 507Section
17.2Due 5/05/09
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Reflection

• The interaction that occurs when a wave bounces
  off a surface that it cannot
• pass through.

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Reflection

• Reflection does not change the speed or frequency
  of a wave, but the wave can be flipped upside
  down.

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Reflection at a Boundary

• If reflection occurs at a fixed boundary, then
  the reflected wave will be upside down compared
  to the original wave.

If reflection occurs at a loose boundary, then
the reflected wave will be unchanged.
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Refraction

• The bending of a wave as it enters a new medium
  at an angle.

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Refraction
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Refraction

• When a wave enters a medium at an angle,
  refraction occurs because one side of the wave
  moves more slowly or faster than the other side.

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Diffraction

• The bending of a wave as it moves around an
  obstacle or passes through a narrow opening.

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Diffraction
The bending of a wave as it passes through an
opening or around the edge of an object.
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Diffraction

• A wave diffracts more if its wavelength is large
  compared to the size of an opening or obstacle.

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Interference
Interference occurs when two or more waves come
together. When two crests or two troughs come
together we get a bright line. When a crest and
a trough come together we get a dark line.
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Standing wave

• A wave that appears to stay in one place and does
  not seem to move through a medium.

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Standing Wave

• A standing wave forms only if half a wavelength
  or a multiple of half a wavelength fits exactly
  into the length of a vibrating cord.

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Homework
Section 17.3Due 5/5/09
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Diffraction Grating
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Homework 18-1
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A
D
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F
E
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Homework 18-1
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Homework 18-1






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2
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Homework 18.1










Y
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The Nature of Sound
What is Sound???
Sound is a Longitudinal Wave traveling through
matter.
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Sound from a Tuning Fork
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Sound Waves
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Speed of Sound
Sound is transmitted through matter.
The Velocity of Sound depends on the matter that
carries it.  
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Sound travels at a velocity of 332m/s in air at
0?C.
At 20?C sound travels at 344m/s.
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Speed of Sound
Velocity of Sound through Various Substances at
0?C air 332 m/s water 1454
m/s wood 3828 m/s iron 5103
m/s stone 5971 m/s
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Human Hearing
Frequency of Sound 20 Hz to 20,000 Hz.
Sound above 20,000 Hz - Ultrasonic
Sound less than 20 Hz Subsonic
(Infrasonic)
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Frequency and Pitch

• The frequency of a sound as a listener perceives
  it.

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Ultrasound

• Ultrasound is used in a variety of applications,
  including sonar and ultrasound imaging.

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Sonar

• A technique for determining the distance to an
  object under water.

Sonar stands for sound navigation and ranging.
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Intensity and Loudness
Intensity of Sound Depends on the amplitude of
the wave.
Loudness Describes a persons response to sound
intensity.
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Loudness is measured in Decibels(dB)
For every 10dB change the sound doubles!! 70dB
is twice 60dB 80dB is four times 60dB
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Faintest Sound Heard 0dB Whisper 15dB Rust
ling Leaves 20dB Purring Cat 25dB Averag
e Home 50dB Vacuum Cleaner 75dB Noisy
Restaurant 80dB Power Mower 100dB Chain
Saw 115dB ------Painful -------
120dB Jet Plane Taking Off 150dB
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The Doppler Effect
The change in wave frequency caused by the motion
of the sound source or the motion of the
observer.
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The Doppler Effect
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The Doppler Effect
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The Doppler Effect
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The outer ear gathers and focuses sound into the
middle ear.
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The middle ear receives and amplifies the
vibrations.
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The inner ear uses nerve endings to sense
vibrations and send signals to the brain.
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Sound Reproduction
Electrical Signal
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Music

• Most musical instruments vary pitch by changing
  the frequency of
• standing waves.

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Harmonics

• 1st

2nd
3rd
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Resonance

• The response of a standing wave to another wave
  of the same frequency, will dramatic increase in
  amplitude of the standing wave.

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Homework 17-4
Worksheet 17-4 Due 5/06/09 Test
5/14/09 Project 6/2/09
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Homework
Wordwise/Math Due 5/07/09 Test
5/14/09 Project 6/2/09
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Homework 18-3
SWUP 18-3 Page515 Worksheet Due 5/5/04
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Music to Your Ears
A back and forth motion is set up in a string,
resulting in a regular vibration. The vibration
is called a standing wave the location of the
crests and troughs are always in the same place.
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In a wind instrument, holes are opened and
closed, changing the length of the vibrating
column of air. This changes the size of the
standing wave.
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Noise
Sound with no regular pattern or definite pitch.
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Tone Quality
The differences among sounds of the same pitch
and loudness.
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Music
Musical Sounds Based on a series of notes called
a musical scale.
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Fundamental
Frequency
262Hz
First Overtone

524Hz
Second Overtone

786Hz
Third Overtone

1048Hz
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Harmony
Notes that sound pleasing together. The ratio of
the frequencies of tones that are in harmony
are small whole numbers.
         Notes that are one octave apart.
Middle C and C 524/262 2/1

         Notes E and C 330/262 5/4
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Interference
Constructive Interference Occurs when the
compressions and rarefactions of two or more
waves come together.
Louder Sound
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Interference
Destructive Interference Occurs when a
compression of one wave arrives at the same time
as a rarefaction of another wave.
Quieter Sound
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Interference
Beats The result of compressions and rarefactions
of two slightly different frequencies reaching
your ears together.
Beats
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Acoustics
The study of the science of sound.
Design auditoriums.
Design communication systems.
Study materials.
Study hearing...... 
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Reverberation
The result of many different reflections of sound
in a large room.
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Speed of Sound
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Speed of Sound
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Homework 18-4
SWUP 18-3 Pg515 SWUP 18-4,Pg521
Worksheet Due 5/5/04 Test 5/6/05
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Homework 18-5
Vocabulary Pg523 Mult. Choice Pg524 Due
5/10/04 Test 5/6/05
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Homework 18-6
Review Questions 11-24, Due 4/11/04 Test 5/6/05