Waves and Sound
Mechanical Waves
When something moves back and forth, side to side, or up and down, we say it vibrates. A vibration is a wiggle.
Wave A disturbance or vibration propagated from point
to point in a medium or in space. ▪ Sound – the vibration of matter ▪ No matter means no sound
▪ Light - vibrations of electric and magnetic fields Partner – pencil and paper demo??
When the bob vibrates up and down, a marking pen traces out a sine curve on paper that moves horizontally at constant speed. When the bob vibrates up and down, a marking pen traces out a sine curve on paper that moves horizontally at constant speed.
Crests – high points Troughs – low points Nodal line The “home” or base position of the medium
before the wave passes through.
Amplitude For a wave or vibration, the maximum displacement
on either side of the equilibrium (Home) position.
Wavelength (l-meters)
The distance between successive crests, troughs, or
identical parts of a wave.
Frequency (f- Hertz (Hz)) For a vibrating body or medium, the number of
vibrations per unit time. For a wave, the number of crests that pass a particular point per unit time.
Hertz The unit of
frequency. One hertz (symbol Hz) equals one vibration per second. Electrons in the transmitting antenna vibrate 96,300,000 times each second and produce 96.3-MHz radio waves.
Period The time required for a vibration or a wave to
make a complete cycle; equal to 1/frequency.
An electric toothbrush completes 90 cycles every second. What are (a) its frequency and (b) its period?
a) 90 cycles per second, 90Hz b) 1/90 sec
Gusts of wind cause the Sears Building in Chicago to sway back and forth, completing a cycle every ten seconds. What are (a) its frequency and (b) its period? a) 1/10 Hz b) 10 sec
Energy is carried by a wave. The matter moves very little. Speed of sound is about 340 meters per second. ▪ The wave travels that fast, not the air itself.
Wave speed = frequency
x
wavelength
V = fl
If the wavelength is 1 m, and one wavelength per second passes the pole, then the speed of the wave is 1 m/s.
If a train of freight cars, each 10 m long, rolls by you at the rate of three cars each second, what is the speed of the train? 30 m/s. We can see this in two ways. ▪ (1) According to the speed definition from Chapter 2, v = d/t = (3 × 10 m)/1 s = 30 m/s, because 30 m of train passes you in 1 s. ▪ (2) If we compare the train to wave motion, with wavelength corresponding to 10 m and frequency 3 Hz, then Speed = frequency × wavelength = 3 Hz × 10 m = 30 m/s.
If a water wave vibrates up and down three times each second and the distance between wave crests is 2 m, what are (a) the wave’s frequency? (b) its wavelength? (c) its wave speed? (a) 3 Hz;
(b) 2 m; (c) Wave speed = frequency × wavelength = 3/s × 2
m = 6 m/s.
Transverse wave A wave in which the medium vibrates in a
direction perpendicular (transverse) to the direction in which the wave travels. Light is an example of a transverse wave.
Longitudinal wave A wave in which the medium vibrates in a
direction parallel (longitudinal) to the direction in which the wave travels. Sound is an example of a longitudinal wave.
Compression The compressed part of the wave
Rarefaction The stretched portion of the wave
Surface waves A wave that travels along a surface separating two
media. Ocean waves are an example of a surface wave.
Sound wave A longitudinal vibratory disturbance
that travels in a medium and can be heard by the human ear when in the approximate frequency range 20 20,000 hertz.
Most sound travels through air, but any elastic substance can transmit sound. Water, steel, etc.
Our subjective impression about the frequency of sound is described as pitch. ▪ Different Tuning forks (notes)
Human hearing is from about 20Hz – 20,000 Hz Infrasonic – below 20Hz
Ultrasonic – above 20,000Hz
tnsetup.exe http://www.youtube.com/watch?v=2G9Q-r2leyw
Intensity The rate at which a wave’s energy flows through a
given area. ▪ Depends on the amplitude and distance from the source
Decibel (dB) The unit of sound intensity ▪ Every 10 dB is ten times more energy ▪ 20 dB is 100 times louder than a 0 dB sound.
Loudness-
Sound
The physical response to sound
Jet engine at 3m
140
Threshold of pain
130
Rock concert
120
Accelerating motorcycle at 5m
110
Pneumatic hammer at 2m
100
Noisy factory
90
Vacuum cleaner
80
Busy traffic
70
Quiet restaurant Residential area at night Empty movie house
50
intensity
▪ Depends on intensity, ear health, brain interpretation.
Rustling of leaves Human breathing (at 3m) Threshold of hearing(good ears)
dB-SPL
40
30 20 10
0
Do compressions and rarefactions in a sound wave travel in the same direction or in opposite directions from one another? They travel in the same direction.
What is the approximate distance of a thunderstorm when you note a 3-s delay between the flash of lightning and the sound of thunder? (Use 340 m/s for the speed of sound.) In 3 s the sound travels (340 m/s × 3 s) = 1020 m
Echo The reflection of sound ▪ Best on hard smooth surfaces ▪ Some gets transmitted ▪ Some gets absorbed ▪ Soft surfaces?
Reverberation Multiple, unwanted echoes
Acoustics The study of sound
The angle of incident sound is equal to the angle of reflected sound.
SONAR originally an acronym for SOund Navigation And
Ranging is a technique that uses sound propagation (usually underwater) to navigate, communicate with or detect other vessels
A depth-sounding vessel surveys the ocean bottom with ultrasonic sound that travels 1530 m/s in seawater. How deep is the water if the time delay of the echo from the ocean floor is 2 s? The 2 s delay means it takes 1 s for the sound to
reach the bottom (and another 1 s to return). Sound traveling at 1530 m/s for 1 s tells us the bottom is 1530 m deep.
Refraction The bending of a wave
as it passes either through a nonuniform medium or from one medium to another, caused by differences in wave speed. Turning a wheelchair, tank, ZTR mower
Forced vibration The setting up of vibrations in an object by a
vibrating force. ▪ Tuning fork on table, machine vibrating the floor ▪ Vibration stops when the source is removed ▪ Vibrations match those of the source.
Natural frequency A frequency at which an elastic object naturally
tends to vibrate, so that minimum energy is required to produce a forced vibration or to continue vibration at that frequency ▪ Bells ▪ Tuning forks ▪ Almost anything will have its own natural frequency ▪ Demo coins, rods, wrenches.
Resonance The response of a body when a forcing frequency
matches its natural frequency. ▪ ▪ ▪ ▪ ▪
Sounding again, resounding A dramatic increase in amplitude occurs Swinging- pushes in rhythm create higher swing Singing in the shower Tuning a radio ▪ ▪ ▪ ▪ ▪
Demo tuning forks Wine glass http://www.youtube.com/watch?v=phqymc8anO0 Tacoma Narrows Bridge Universal_Newsreel_Welcomes_Telenews_to_Tacoma__Tacoma_Bri dge_Catastrophe.asf
Interference The result of superimposing two or more waves of
the same wavelength.
Constructive interference Results from crest-to- crest
Destructive interference results from crest-to-
reinforcement
trough cancellation
▪ Jumping on a trampoline
▪ Noise cancelling headphones ▪ Demo speakers
Beats A series of alternate reinforcements
and cancellations produced by the interference of two waves of slightly different frequency, heard as a throbbing effect in sound waves. ▪ Demo tuning forks
Standing wave A stationary wave pattern formed in a medium
when two sets of identical waves pass through the medium in opposite directions. ▪ Nodes – stationary part ▪ Antinode – largest movement
Is it possible for one wave to cancel another so that no amplitude remains? Yes. This is destructive interference. In a standing
wave in a rope, for example, parts of the rope–the nodes–have no amplitude because of destructive interference.
Doppler effect The change in frequency of wave motion resulting
from motion of the wave source or receiver
Doppler effect applies to all waves
Occurs also when the source is stationary and the listener moves.
With light an increase in frequency is called a blue shift,(moving towards) and a decrease in frequency is called a red shift, (moving away).
When a wave source moves toward you, do you measure an increase or decrease in wave speed? Neither! It is the frequency of the waves that
changes for a moving source, not the wave speed. Be clear about the distinction between frequency and speed. How frequently a wave vibrates is altogether different from how fast it moves from one place to another
A wave barrier is produced when the wave source travels as fast as the waves. Considerable thrust is required to get past this
barrier.
Bow wave The V-shaped wave made by an object moving
across a liquid surface at a speed greater than the wave speed. (THE WAKE)
Shock wave The cone-shaped wave made by an object (even silent)
moving at supersonic speed through a fluid. ▪ A supersonic aircraft usually produces two sonic booms, one from the aircraft's nose (high pressure) and the other from its tail (Low pressure), resulting in a double thump. ▪ Rocket_Power_Sends_Chuck_Yeager_into_Space__The_Sound_ Barrier.asf
Sometimes the barriers can be seen! http://www.youtube.com/watch?v=gWGLAAYd bbc
When something moves back and forth, side to side, or up and down, we say it vibrates. A vibration is a wiggle.
Wave A disturbance or vibration propagated from point
to point in a medium or in space. ▪ Sound – the vibration of matter ▪ No matter means no sound
▪ Light - vibrations of electric and magnetic fields Partner – pencil and paper demo??
When the bob vibrates up and down, a marking pen traces out a sine curve on paper that moves horizontally at constant speed. When the bob vibrates up and down, a marking pen traces out a sine curve on paper that moves horizontally at constant speed.
Crests – high points Troughs – low points Nodal line The “home” or base position of the medium
before the wave passes through.
Amplitude For a wave or vibration, the maximum displacement
on either side of the equilibrium (Home) position.
Wavelength (l-meters)
The distance between successive crests, troughs, or
identical parts of a wave.
Frequency (f- Hertz (Hz)) For a vibrating body or medium, the number of
vibrations per unit time. For a wave, the number of crests that pass a particular point per unit time.
Hertz The unit of
frequency. One hertz (symbol Hz) equals one vibration per second. Electrons in the transmitting antenna vibrate 96,300,000 times each second and produce 96.3-MHz radio waves.
Period The time required for a vibration or a wave to
make a complete cycle; equal to 1/frequency.
An electric toothbrush completes 90 cycles every second. What are (a) its frequency and (b) its period?
a) 90 cycles per second, 90Hz b) 1/90 sec
Gusts of wind cause the Sears Building in Chicago to sway back and forth, completing a cycle every ten seconds. What are (a) its frequency and (b) its period? a) 1/10 Hz b) 10 sec
Energy is carried by a wave. The matter moves very little. Speed of sound is about 340 meters per second. ▪ The wave travels that fast, not the air itself.
Wave speed = frequency
x
wavelength
V = fl
If the wavelength is 1 m, and one wavelength per second passes the pole, then the speed of the wave is 1 m/s.
If a train of freight cars, each 10 m long, rolls by you at the rate of three cars each second, what is the speed of the train? 30 m/s. We can see this in two ways. ▪ (1) According to the speed definition from Chapter 2, v = d/t = (3 × 10 m)/1 s = 30 m/s, because 30 m of train passes you in 1 s. ▪ (2) If we compare the train to wave motion, with wavelength corresponding to 10 m and frequency 3 Hz, then Speed = frequency × wavelength = 3 Hz × 10 m = 30 m/s.
If a water wave vibrates up and down three times each second and the distance between wave crests is 2 m, what are (a) the wave’s frequency? (b) its wavelength? (c) its wave speed? (a) 3 Hz;
(b) 2 m; (c) Wave speed = frequency × wavelength = 3/s × 2
m = 6 m/s.
Transverse wave A wave in which the medium vibrates in a
direction perpendicular (transverse) to the direction in which the wave travels. Light is an example of a transverse wave.
Longitudinal wave A wave in which the medium vibrates in a
direction parallel (longitudinal) to the direction in which the wave travels. Sound is an example of a longitudinal wave.
Compression The compressed part of the wave
Rarefaction The stretched portion of the wave
Surface waves A wave that travels along a surface separating two
media. Ocean waves are an example of a surface wave.
Sound wave A longitudinal vibratory disturbance
that travels in a medium and can be heard by the human ear when in the approximate frequency range 20 20,000 hertz.
Most sound travels through air, but any elastic substance can transmit sound. Water, steel, etc.
Our subjective impression about the frequency of sound is described as pitch. ▪ Different Tuning forks (notes)
Human hearing is from about 20Hz – 20,000 Hz Infrasonic – below 20Hz
Ultrasonic – above 20,000Hz
tnsetup.exe http://www.youtube.com/watch?v=2G9Q-r2leyw
Intensity The rate at which a wave’s energy flows through a
given area. ▪ Depends on the amplitude and distance from the source
Decibel (dB) The unit of sound intensity ▪ Every 10 dB is ten times more energy ▪ 20 dB is 100 times louder than a 0 dB sound.
Loudness-
Sound
The physical response to sound
Jet engine at 3m
140
Threshold of pain
130
Rock concert
120
Accelerating motorcycle at 5m
110
Pneumatic hammer at 2m
100
Noisy factory
90
Vacuum cleaner
80
Busy traffic
70
Quiet restaurant Residential area at night Empty movie house
50
intensity
▪ Depends on intensity, ear health, brain interpretation.
Rustling of leaves Human breathing (at 3m) Threshold of hearing(good ears)
dB-SPL
40
30 20 10
0
Do compressions and rarefactions in a sound wave travel in the same direction or in opposite directions from one another? They travel in the same direction.
What is the approximate distance of a thunderstorm when you note a 3-s delay between the flash of lightning and the sound of thunder? (Use 340 m/s for the speed of sound.) In 3 s the sound travels (340 m/s × 3 s) = 1020 m
Echo The reflection of sound ▪ Best on hard smooth surfaces ▪ Some gets transmitted ▪ Some gets absorbed ▪ Soft surfaces?
Reverberation Multiple, unwanted echoes
Acoustics The study of sound
The angle of incident sound is equal to the angle of reflected sound.
SONAR originally an acronym for SOund Navigation And
Ranging is a technique that uses sound propagation (usually underwater) to navigate, communicate with or detect other vessels
A depth-sounding vessel surveys the ocean bottom with ultrasonic sound that travels 1530 m/s in seawater. How deep is the water if the time delay of the echo from the ocean floor is 2 s? The 2 s delay means it takes 1 s for the sound to
reach the bottom (and another 1 s to return). Sound traveling at 1530 m/s for 1 s tells us the bottom is 1530 m deep.
Refraction The bending of a wave
as it passes either through a nonuniform medium or from one medium to another, caused by differences in wave speed. Turning a wheelchair, tank, ZTR mower
Forced vibration The setting up of vibrations in an object by a
vibrating force. ▪ Tuning fork on table, machine vibrating the floor ▪ Vibration stops when the source is removed ▪ Vibrations match those of the source.
Natural frequency A frequency at which an elastic object naturally
tends to vibrate, so that minimum energy is required to produce a forced vibration or to continue vibration at that frequency ▪ Bells ▪ Tuning forks ▪ Almost anything will have its own natural frequency ▪ Demo coins, rods, wrenches.
Resonance The response of a body when a forcing frequency
matches its natural frequency. ▪ ▪ ▪ ▪ ▪
Sounding again, resounding A dramatic increase in amplitude occurs Swinging- pushes in rhythm create higher swing Singing in the shower Tuning a radio ▪ ▪ ▪ ▪ ▪
Demo tuning forks Wine glass http://www.youtube.com/watch?v=phqymc8anO0 Tacoma Narrows Bridge Universal_Newsreel_Welcomes_Telenews_to_Tacoma__Tacoma_Bri dge_Catastrophe.asf
Interference The result of superimposing two or more waves of
the same wavelength.
Constructive interference Results from crest-to- crest
Destructive interference results from crest-to-
reinforcement
trough cancellation
▪ Jumping on a trampoline
▪ Noise cancelling headphones ▪ Demo speakers
Beats A series of alternate reinforcements
and cancellations produced by the interference of two waves of slightly different frequency, heard as a throbbing effect in sound waves. ▪ Demo tuning forks
Standing wave A stationary wave pattern formed in a medium
when two sets of identical waves pass through the medium in opposite directions. ▪ Nodes – stationary part ▪ Antinode – largest movement
Is it possible for one wave to cancel another so that no amplitude remains? Yes. This is destructive interference. In a standing
wave in a rope, for example, parts of the rope–the nodes–have no amplitude because of destructive interference.
Doppler effect The change in frequency of wave motion resulting
from motion of the wave source or receiver
Doppler effect applies to all waves
Occurs also when the source is stationary and the listener moves.
With light an increase in frequency is called a blue shift,(moving towards) and a decrease in frequency is called a red shift, (moving away).
When a wave source moves toward you, do you measure an increase or decrease in wave speed? Neither! It is the frequency of the waves that
changes for a moving source, not the wave speed. Be clear about the distinction between frequency and speed. How frequently a wave vibrates is altogether different from how fast it moves from one place to another
A wave barrier is produced when the wave source travels as fast as the waves. Considerable thrust is required to get past this
barrier.
Bow wave The V-shaped wave made by an object moving
across a liquid surface at a speed greater than the wave speed. (THE WAKE)
Shock wave The cone-shaped wave made by an object (even silent)
moving at supersonic speed through a fluid. ▪ A supersonic aircraft usually produces two sonic booms, one from the aircraft's nose (high pressure) and the other from its tail (Low pressure), resulting in a double thump. ▪ Rocket_Power_Sends_Chuck_Yeager_into_Space__The_Sound_ Barrier.asf
Sometimes the barriers can be seen! http://www.youtube.com/watch?v=gWGLAAYd bbc
