Transcript Waves and Sound - ELECTRA ISD Electra, Texas

Waves and Sound
Intro
A. Pick up your notes and worksheet packets
B. Write the following questions on a blank piece of paper
(don’t answer yet)
1. What is the difference between a mechanical
and electromagnetic wave?
2. What is the difference between a transverse and
longitudinal wave?
3. What do all waves transfer?
4. What don’t waves transfer?
Section 1: Intro to Waves
• Waves
– Are disturbances that move through an empty space
or through medium (material)
– Waves transfer energy without transferring matter.
– Particles of medium move in simple harmonic motion
Mechanical: Through a
medium
Electromagnetic:
Through empty space
• Mechanical wave:
– Caused by a disturbed medium and move by action
reaction of particles
– ex: water wave, sound
• A medium is matter particles like gas (ex. air),
liquid (ex. Water), and solid (ex. earth)
Two types of mechanical waves that require a medium
Transverse
Wave
Longitudinal
Wave
Electromagnetic wave:
• Move through empty space (no medium)
• Created by moving electrons
• Ex. radio waves, microwaves, light
• SOL= 3.0 x 10 8 m/s
Types Electromagnetic Waves
Through empty space
• In order to start and transmit a wave, a
source of disturbance (vibration) and a
disturbed medium are required.
• Mechanical caused by vibrating particles
– Like seen here
• Electromagnetic by vibrating electrons
Damping:
• A decrease in the amplitude of a wave
• Caused by energy loss or the spreading
out of the wave over a larger area.
• Wave pulse is a single wave disturbance
• Wave train (continuous wave) - is a
series of pulses at intervals
Section 2: Types of Mechanical
Waves
Transverse
Longitudinal
Perpendicular to the
direction of travel
Direction of
travel
Transverse Wave:
• Wave particles move perpendicular to the
direction the wave travels
• Ex. vibrating string of a musical instrument
Parts of a transverse wave
Crest
Wavelength (‫)ג‬
amplitude
Equilibrium
Position
Wavelength (‫)ג‬
amplitude
Wavelength (‫)ג‬
Trough
• Crest- highest point on a transverse wave
• Trough- lowest point on a transverse
wave
• Equilibrium position- center around
which simple harmonic motion occurs
• Amplitude- from the equilibrium position
to the crest or trough
Longitudinal Wave:
• Particles vibrate parallel to the direction
the wave travels
• ex. sound wave
Direction of travel
Particles vibrate parallel to the direction of travel
Parts of a Longitudinal Wave:
• Compression- point where the particles
are closest together
• Rarefaction- point where the particles are
furthest apart
Rarefaction
Compression
Intro Questions
1. What do all waves transfer?
2. What don’t waves transfer?
3. What starts a wave?
Pick between the following choices and answer
this correctly:
4. Sound is a (mechanical or electromagnetic)
(transverse or longitudinal) wave.
Section 3: Relationship
between Wavelength,
Frequency and Wave Speed
• velocity ( v ): speed of the wave.
– unit: m/s (meter/second)
• frequency ( f ): vibrations per second of
the wave
– unit: Hz (hertz)
• wavelength ( ‫) ג‬: length of one wave pulse
– unit: m (meter)
Lets revisit our old equation
d
V= ___
t
What is the velocity of an object that moves
25 meters in 3 seconds?
Lets revisit our old equation
d
V= ___
t
What is the velocity of an object that moves
25 meters in 3 seconds?
Now lets look at the new equation you can
use as well.
new
old
d
V= ___
t
Example what is the velocity of a wave that has a
frequency of 3Hz and a wavelength of 5m?
Now lets look at the new equation
you can use as well
new
old
d
V= ___
t
Now lets look at the new equation
you can use as well
new
old
d
V= ___
t
Now lets look at the new equation
you can use as well
new
old
d
V= ___
t
Now lets look at the new equation
you can use as well
new
old
d
V= ___
t
Relationship between frequency and
wavelength.
• Wavelength and frequency are inversely
related
• As frequency goes up the wavelength gets
shorter (assuming no change in velocity)
Click for animation
Period (T) vs. Frequency (f)
• Period (T) – seconds for one cycle
– (unit s)
• Frequency (f) – cycles for one second
– (unit Hz)
• If you know one you can solve for the other
Example 1
Wave Math
The frequency of a wave is 560 Hz. What is
its period?
The frequency of a wave is 560 Hz. What is
its period?
Example 2
Wave Math
A girl floats in the ocean and watches 12
wave crests pass her in 46 s. Calculate the
wave: a) frequency
b) period
A girl floats in the ocean and watches 12
wave crests pass her in 46 s. Calculate the
wave: a) frequency
b) period
Example 3
Wave Math
The period of a wave is 0.044s. How many
cycles will the energy source make in 22s?
cycles
second
The period of a wave is 0.044s. How many
cycles will the energy source make in 22s?
Example 4
Wave Math
A distance of 0.33 m separates a wave crest from
the adjacent trough, and the vertical distance from
the top of a crest to the bottom of a trough is
0.24m.
A. What is the wavelength?
B. What is the amplitude?
0.33m
0.24m
Example 4
Wave Math
A distance of 0.33 m separates a wave crest from
the adjacent trough, and the vertical distance from
the top of a crest to the bottom of a trough is
0.24m.
A. What is the wavelength?
B. What is the amplitude?
0.33m
0.66m
Example 4
Wave Math
A distance of 0.33 m separates a wave crest from
the adjacent trough, and the vertical distance from
the top of a crest to the bottom of a trough is
0.24m.
A. What is the wavelength?
B. What is the amplitude?
0.24m
0.12m
Example 5
Wave Math
What is the speed of a 256 Hz sound with a
wavelength of 1.35 m?
Example 5
Wave Math
What is the speed of a 256 Hz sound with a
wavelength of 1.35 m?
Example 6
Wave Math
You dip your finger into a pan of water 14 times in
11s, producing wave crests separated by 0.16 m.
A. What is the frequency?
B. What is the period?
C. What is the velocity?
Example 6
Wave Math
You dip your finger into a pan of water 14 times in 11s, producing wave
crests separated by 0.16 m.
A. what is the frequency
B. What is the period
C. Velocity
Assignment to work on:
CP
• Worksheet Packet Section 3
Honors
• Worksheet Packet Section 3
• Book Problems 4,5,6 pg 486-487
Pendulum Lab day: Your into is to read over
your lab; I will ask you if there are any questions soon
Length (L)
Amplitude (A)
Equilibrium
Position
Pendulum Lab day
One complete cycle
Intro after pendulum lab
All labs are due today:
Turn them in on my desk
1. Your pendulum makes 5 complete cycles in 10
seconds.
a. What is the pendulums frequency?
b. What is the pendulums period?
2. What is the definition of frequency (can be in
equation form)
3. When you increase the length of the pendulum
string, what happens to frequency?
Section 4: The Pendulum
• Pendulum- a weight on a string that
moves in simple harmonic motion (swings
back and forth).
This is the
equilibrium
position.
accelerating
decelerating
• Movement from a to c and back to a is one
complete cycle or vibration
• Simple harmonic motion- vibration about
an equilibrium position
– Constant back and forth motion over the
same path.
– 15º is the maximum angle for a pendulum to
have simple harmonic motion where our
equations work
• Masses do not effect the period in simple
harmonic motion.
• What effects the period:
• L – length of the string
• g – acceleration due to gravity
Click here to interact with a
pendulum
Example 7
A tall tree sways back and forth in the
breeze with a frequency of 2Hz. What is the
period of this tree?
Example 7
A tall tree sways back and forth in the
breeze with a frequency of 2Hz. What is the
period of this tree?
Example 8
Hypnotist Paulbar the great swings his
watch from a 0.20 m chain in front of a
subjects eyes. What is the period of swing
of the watch.
Example 8
Hypnotist Paulbar the great swings his
watch from a 0.20 m chain in front of a
subjects eyes. What is the period of swing
of the watch.
Example 9
A spider swings slightly in the breeze from a
silk thread that is 0.09 m in length. What is
the period of the simple harmonic motion?
Example 9
A spider swings slightly in the breeze from a
silk thread that is 0.09 m in length. What is
the period of the simple harmonic motion?
Example 10
If a pendulum is shortened, does the period
increase or decrease? What about its
frequency?
Example 10
If a pendulum is shortened, does the period
increase or decrease? What about its
frequency?
Period decreases
Frequency increases
• Finish section 4 of the worksheets and
turn in your packet today when you are
done.
• Work on something else quietly while you
wait for everyone to complete their work
Section 5: Wave Interactions
•
•
•
•
Reflection
Refraction
Diffraction
Interference
Reflection:
• The turning back of a wave at the
boundary of a new medium
• Ex: light off a mirror, or sound echo
• Incident wave- incoming
• Waves reflected off a fixed boundary are
inverted.
– A fixed boundary is one not allowed to move
• Waves reflected off a flexible boundary are
upright.
– A flexible boundary is allowed to move
Law of Reflection:
• Angle of reflection of a wave equals angle
of incidence
• θr = θi
Normal line
θi
θr
• Normal line – line perpendicular to surface
being reflected off of.
Example 11
• Draw the reflected wave, labeling angles
of incidence, reflection, and the normal
line
35º
Wave front:
• Portion of a medium’s surface in which
particles are in phase
• Particles in phase are in the same stage of
their vibration.
Example 12
• Which two of these particles would be in
phase?
Refraction:
• the bending of a wave path as it enters a
new medium obliquely (indirectly)
• caused by difference in speed of the new
medium
• fast to slow – bends toward the normal line
• slow to fast – bends away from normal
Refraction
• Light travels slower in water
θr
θi
Normal
Line
slow
Fast
medium
Example 13
• Draw the refracted wave, labeling the
normal line, angle of incidence, and angle
of refraction.
Slow
Fast
Example 13
• Draw the refracted wave, labeling the
normal line, angle of incidence, and angle
of refraction.
Normal line
θi
θr
Slow
Fast
Diffraction:
• Spreading of waves
around edges or through
an opening of a boundary
• Is greatest when size of
opening is smaller than
wavelength
Principle of Superposition:
• Displacement of a medium by two or more
waves is the algebraic sum of the
displacements of the waves alone
Interference:
• Result of the superposition of two
or more waves
• constructive- (crest meets crest
or trough meets trough)
amplitudes add
• destructive – (crest meets
trough) amplitudes subtract
• Only temporary as paths cross
Constructive interference
Only temporary as paths cross
Destructive interference
Only temporary as paths cross
Constructive and destructive
interference in two sine waves
Example 14 (finish off the drawings)
Before
Constructive interference
Destructive interference
During
After
Wave Fronts Interfering
Antinodal line
Lines of constructive
interference
Nodal line
Lines of destructive
interference
Standing wave:
• created by waves with same
frequency, wavelength, and
amplitude traveling in opposite
directions and interfering.
• consists of nodes (o amplitude)
and antinodes (max amplitude)
• produced by certain frequencies
Standing Waves
Being Produced
Antinode
Node
Show what you know
1. Refraction happens when waves –
a) Turn back at a boundary
b) Enter a new medium at an angle.
c) Go through an opening.
d) Are superpositioned.
2. This diagram shows which wave
interaction?
a) Reflection
b) Refraction
c) Diffraction
d) Interference
3. Constructive interference occurs whena) Crest meets crest
b) Trough meets trough
c) Amplitudes add up
d) All of these
4. A line along which the medium does not
vibrate is called a
a) Nodal line
b) Antinodal line
c) Construction
5. Standing waves are produced by waves
of equal ________ traveling in opposite
directions.
a) Wavelength
b) Frequency
c) Amplitude
d) All of the above
Intro Questions
1.
An echo bouncing off a nearby wall tends to
________________ back toward the source.
2. A pendulum requires 3 seconds to make one back and
forth motion. Calculate the pendulum’s frequency?
3. Steam is rising from a cup of hot tea. What type of
thermal energy transfer is occurring? (conduction,
convection, or radiation)
4. What type of interference would occur when these waves
meet?
5. A water wave has a speed of 5m/s and the distance
between each crest is 2.0m. What is the frequency of
the water wave?
Section 6: Sound
• Sound waves are produced by a vibrating
object
• Sound waves are longitudinal mechanical
waves.
Sound Frequency:
• Determines pitch
• 20 – 20,000 Hz are audible
to an average person
• Less than 20 Hz are
infrasonic
• Greater than 20,000 Hz are
ultrasonic
Uses of ultrasonic waves
More than 20,000 Hz- Ultrasonic waves
Echolocation and Sonar
• Sonar is simply making use of
an echo.
• An echo is used to locate an
object.
• When an animal or machine makes a noise, it sends sound
waves into the environment around it.
• Those waves bounce off nearby objects, and some of them
reflect back to the object that made the noise.
• Whales, Dolphins, Bats, and many more organisms use
sound for locating prey and predators
Less than 20 Hz- Subsonic or
Infrasonic Sound
Sound Velocity
• Largely depends on medium
elasticity
• Solids>liquids>gasses
• Then depends on temperature
– Faster at higher temperatures
– Air (at 0ºC) v = 331 m/s and +/0.6 m/s per ºC
Generally between phases
vsolids > vliquids > vgases
Sound Velocity Equations
v = 331 + 0.6 Tc
v = d/t
v = fλ
Interesting sound facts
• Sound travels 15 times faster in the steel from a
railroad track.
• Sound travels 4 times faster in water
• At sea level, the speed of sound is 340 m/s or 760
mi/hr. This is called mach 1.
The speed of sound will be the same for all
frequencies under the same conditions.
– Wavelength and frequency are inversely
related
– As frequency goes up the wavelength gets
shorter
Example 15
What is the speed of sound at room
temperature (22ºC)
What is the speed of sound at room
temperature (22ºC)
Example 16
How many seconds will it take to hear an
echo if you yell toward a mountain 110 m
away on a day when air temperature is 6.0 ºC?
How many seconds will it take to hear an echo if you yell
toward a mountain 110 m away on a day when air
temperature is -6.0 ºC?
Example 17
If sound travels at 340 m/s, how many
seconds will it take thunder to travel
1609m?
Example 17
If sound travels at 340 m/s, how many seconds will it take thunder to
travel 1609m?
Example 18
A sonar echo takes 3.1s to go to a
submarine and back to the ship. If sound
travels at 1400m/s in water, how far
away is the submarine?
Example 18
A sonar echo takes 3.1s to go to a submarine and back to the ship. If
sound travels at 1400m/s in water, how far away is the
submarine?
Example 19
On a day when air temperature is 11ºC, you
use a whistle to call your dog. If the
wavelength of the sound produced is
0.015m, what is the frequency? Could
you hear the whistle?
Example 19
On a day when air temperature is 11ºC, you use a whistle to call your
dog. If the wavelength of the sound produced is 0.015m, what is
the frequency? Could you hear the whistle?
Intro
1. A 25,000Hz dog whistle can be heard by a dog but not by humans
because the frequency is in the ______________ range.
2. An elephant can hear below 20 Hz. This is the _________ range.
3. The range we can hear is between _____ and _______ and we call
this range ______________.
4. Which of the following will sound travel fastest in?
a) a swimming pool
b) a steel bridge
c) a vacuum
d) warm air
5. Sound wave A has twice the frequency of sound wave B. That
means that sound wave A must _______________
a) travel faster than sound wave B
b) have a shorter wavelength than sound wave B
c) have a lower pitch that sound wave B
d) be louder than sound wave B
Section 7: The Doppler Effect
Doppler Effect
• Change in pitch caused by relative motion
of source and observer
• Pitch increases as sound and observer
approach (and vice versa)
• Doppler Effect Example
• http://www.animations.physics.unsw.edu.a
u/jw/doppler.htm#example
Examples/Uses
• Doppler radar: detects storm fronts and
their approach speed.
Radar Gun
Doppler Effect Problems
• Frequency rises when its coming closer
and lowers when moving away.
Example 20
Sitting on a beach at Coney Island one
afternoon, Sunny finds herself beneath the
flight path of airplanes leaving Kennedy
Airport. What frequency will Sunny hear
as a jet, whose engines emit sound at a
frequency of 1000 Hz, flies towards her at
a speed of 100.0 m/s? (use 340 m/s as the
speed of sound)
Example 20
Sitting on a beach at Coney Island one afternoon, Sunny finds herself
beneath the flight path of airplanes leaving Kennedy Airport. What
frequency will Sunny hear as a jet, whose engines emit sound at a
frequency of 1000 Hz, flies towards her at a speed of 100.0 m/s?
(use 340 m/s as the speed of sound)
Example 21
Sitting on a beach at Coney Island one
afternoon, Sunny finds herself beneath the
flight path of airplanes leaving Kennedy
Airport. What frequency will Sunny hear
as a jet, whose engines emit sound at a
frequency of 1000 Hz, flies away from her
at a speed of 100.0 m/s? (use 340 m/s as
the speed of sound)
Example 21
Sitting on a beach at Coney Island one afternoon, Sunny finds herself
beneath the flight path of airplanes leaving Kennedy Airport. What
frequency will Sunny hear as a jet, whose engines emit sound at a
frequency of 1000 Hz, flies away from her at a speed of 100.0 m/s?
(use 340 m/s as the speed of sound)
Example 22
A sparrow chases a crow with a speed of
4.0 m/s, while chirping at a frequency of
850.0 Hz. What frequency of sound does
the crow hear as he flies away from the
sparrow at a speed of 3.0 m/s? (use 340
m/s as the speed of sound)
Example 22
A sparrow chases a crow with a speed of 4.0 m/s, while chirping at a
frequency of 850.0 Hz. What frequency of sound does the crow
hear as he flies away from the sparrow at a speed of 3.0 m/s? (use
340 m/s as the speed of sound)
Intro
You are chasing after your parent’s car because you forgot
your lunch in it. You are running at a swift 4.0 m/s and
your parent is going 12 m/s. It is a cold 5.0° C today
and your voice is producing a frequency of 460 Hz.
Your parent’s car is squealing a bit and producing a
frequency of 760 Hz.
1.
What frequency would your parent hear you at if
he/she could?
2.
What frequency do you hear your parent’s car at?
You are chasing after your parent’s car because you forgot your lunch
in it. You are running at a swift 4.0 m/s and your parent is going
12 m/s. It is a cold 5.0° C today and your voice is producing a
frequency of 460 Hz. Your parent’s car is squealing a bit and
producing a frequency of 760 Hz.
1.
What frequency would your parent hear you at if he/she could?
You are chasing after your parent’s car because you forgot your lunch
in it. You are running at a swift 4.0 m/s and your parent is going
12 m/s. It is a cold 5.0° C today and your voice is producing a
frequency of 460 Hz. Your parent’s car is squealing a bit and
producing a frequency of 760 Hz.
2. What frequency do you hear your parent’s car at?
Section 8: Intensity and Perceived
Sound
• The property of sound
waves associated with
loudness is amplitude
• The property associated
with pitch is frequency
• Sound Intensity is the rate of transferring
energy through an area
The Decibel Scale
• Threshold of hearing (Io)– the minimum intensity
sound that can be heard at
certain frequencies
Io= 1.0 x 10-12
ß = 0 dB at the threshold of
hearing
More on the Decibel Scale
• The decibel scale relates sound intensity to
human hearing
– An intensity of 0 dB is when there is enough energy
for an average human to detect the sound
– 1-dB in intensity level is the smallest change in
loudness that an average listener can detect
– If the relative intensity level increases by 10 dB, the
new sound seems approximately twice as loud as the
original sound.
Section 9: Resonance and Music
Resonance in Music
• Forced Vibration- The vibration of an
object that is made to vibrate by
another vibrating object.
• Sympathetic vibrations- secondary
vibrations caused by forced vibration
of a first object.
• Sounding board- part of an
instrument forced into vibration to
amplify sound
Example of creating forced
vibrations to make a sound louder
• Sounding board of a musical instrument.
• Example: guitar makes a strings vibrations
resonate
Resonance:
• Also called sympathetic vibrations
• Dramatic increase in the amplitude of a
wave when the frequency of an applied
force matches the natural frequency of the
object.
Resonance can be dangerous
• Wind caused the Tacoma Narrows suspension
bridge to vibrate at its natural frequency.
• The amplitude of the vibrations caused too much
strain on the bridge until it collapsed.
Difference between music and noise
• Noise- a random mixture of a large
number of sound frequencies
• Music- Sound frequency or mixture of
frequencies with a pattern
Percussion Instrument:
• Musical sound produced
by striking the object
• Frequency depends on
the mass of the object.
• To raise the pitchdecrease the mass of the
object.
• Ex- drums, xylophone,
bells
Stringed Instrument
• Musical sound produced by
plucking or blowing strings
• Frequency depends on four
factors
• To raise pitch
– 1. decrease diameter of
string
– 2. increase tension
– 3 decrease length
– 4. decrease density of string
material
• Examples: guitar, violin
Wind Instrument
• Musical sound
produced by vibrating
air column
• Frequency depends
mainly on length of air
column
• To raise pitchdecrease the size of the
air column
• Examples- oboe, flute
• Standing Waves are formed
in the instrument due to
vibrations
• When the natural frequency
is hit the sound amplifies
Open Ended Wind Column Instrument
• Must be nodes at both
ends
Closed Ended Wind Column Instrument
• There is an antinode
at the closed end.
• Count standing waves
by including the return
trip.
• Acoustics- field of study related to sound
• Acoustic designers try to maximize the
quality of sound reaching the audience
– Control the size, shape, and material used
– They try and control the reflection
Two types of reflection with sound
• Reverberation- If a reflected sound wave
reaches the ear within 0.1 seconds of the
initial sound, then it seems to the person
that the sound is prolonged.
• Echoes- A perceived second sound that
arrives after the first has died out.
– Echoes occur when a reflected sound wave
reaches the ear more than 0.1 seconds after
the original sound wave was heard.
• Interference causes beats
– Beats occur due to constructive and
destructive interference between sounds with
close but not exact frequencies.