Transcript Waves and Sound - Hingham Schools

Waves and Sound
Chapter 14
Characteristics of Waves
Waves: A rhythmic disturbance
that carries energy.
Medium: A material through
which waves travel.
Transverse Wave
A wave in which the medium moves
at a right angle to the direction the
wave is traveling.
Amplitude
Crest
Trough
Wavelength
Crest
Trough
Crest: The top of the wave.
Trough: The bottom or valley of the
wave.
Amplitude
Amplitude: The greatest distance the
particles in a wave rise or fall from
their rest position. The energy by the
wave depends on the amplitude.
Wavelength(- lambda, m): The
distance between a point on one wave
and the same identical point on the next
wave.
v
Wave Velocity(v, m/s): The distance
traveled by any point on the wave in one
second.
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.
v

velocity = wavelength X frequency
v =  x f
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
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
v = 0.75m/s
Find: f
Basic Equation: v =  X f
Solve: f = v / 
= (0.75m/s)
(1.20m)
f = 0.63Hz
Homework #14-1
Read & Take Notes
Pages: 329-333
Practice Problems: 1-7
Page:335
Due: 5/7/7
The Nature of Sound
What is Sound???
Sound is a Compression Wave
traveling through matter.
Compressional Waves
Compression Waves
Matter vibrates in the same
direction as the wave travels.
Compressional Waves
Compression
Rarefaction
Comparing Media
Speed of Sound
Sound is transmitted
through matter
.
The Velocity of Sound
depends on the
Sound travels at a velocity of
332m/s in air at 0C.
•Sound travels faster through warm air
than through cold air.
•The velocity of sound increases about
0.6m/s for each degree in temperature.
•At 20C sound travels at 344m/s.
•Sound travels much faster through liquids
and solids than through gases.
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
Human Hearing
Frequency of Sound
20 Hz to 20,000 Hz.
Sound above 20,000 Hz - Ultrasonic
Sound less than 20 Hz – Subsonic
(Infrasonic)
Intensity and Loudness
Intensity of Sound
Depends on the amplitude
of the wave.
Loudness
Describes a person’s response
to sound intensity.
Loudness is measured in
Decibels(dB)
For every 10dB change
the sound doubles!!
70dB is twice 60dB
80dB is four times 60dB
Faintest Sound Heard
Whisper
Rustling Leaves
Purring Cat
Average Home
Vacuum Cleaner
Noisy Restaurant
Power Mower
Chain Saw
------Painful ------Jet Plane Taking Off
0dB
15dB
20dB
25dB
50dB
75dB
80dB
100dB
115dB
120dB
150dB
The Doppler Effect
The change in wave frequency
caused by the motion of the
sound source or the motion
of the observer.
The Doppler Effect
The Doppler Effect
Homework #15-1
PP: 1-4 Page: 352
Section Review
Page:355
Due: 5/11/01
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.
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.
Noise
Sound with no regular pattern or
definite pitch.
Tone Quality
The differences among sounds of
the same pitch and loudness.
Music
Musical Sounds
Based on a series of notes
called a musical scale.
Fundamental
Frequency
262Hz
First
Overtone
524Hz
Second
Overtone
786Hz
Third
Overtone
1048Hz
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
Interference
Constructive Interference
Occurs when the compressions
and rarefactions of two or
more waves come together.
Louder
Sound
Interference
Destructive Interference
Occurs when a compression of one
wave arrives at the same time as a
rarefaction of another wave.
Quieter
Sound
Interference
Beats
The result of compressions and
rarefactions of two slightly
different frequencies reaching
your ears together.
Beats
Acoustics
The study of the science of sound.
Design auditoriums.
Design communication systems.
Study materials.
Study hearing......
Reverberation
The result of many different
reflections of sound in
a large room.
Homework #4-20
SWUP 18-4
Page:521
Worksheet
Due: 5/17/01