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Chapter 14 - SoundChapter 14 - Sound
At the end of the chapter, you should be able to
At the end of the chapter, you should be able to
� Describe the production of sound by vibrating sources.
� Describe the longitudinal nature of sound waves in terms of the processes of compression and rarefaction.
� Explain that a medium is required in order to transmit sound waves and the speed of sound differs in air, liquids and solids.
� Describe the production of sound by vibrating sources.
� Describe the longitudinal nature of sound waves in terms of the processes of compression and rarefaction.
� Explain that a medium is required in order to transmit sound waves and the speed of sound differs in air, liquids and solids.
At the end of the chapter, you should be able to
At the end of the chapter, you should be able to
� Relate loudness of a sound wave to its amplitude and pitch to its frequency.
� Describe how the reflection of sound may produce an echo, and how this may be used for measuring distances.
� Relate loudness of a sound wave to its amplitude and pitch to its frequency.
� Describe how the reflection of sound may produce an echo, and how this may be used for measuring distances.
QuizQuiz
� Elephants have the ‘intuition’ and can ‘hear’ that a storm is approaching from as far as 240 km away. They can also communicate with each other over great distances using sounds that we, human beings, cannot hear.
How is this possible?
� Elephants have the ‘intuition’ and can ‘hear’ that a storm is approaching from as far as 240 km away. They can also communicate with each other over great distances using sounds that we, human beings, cannot hear.
How is this possible?
QuizQuiz
Elephants produces sound that is beyond the human audible frequency range.
Elephants produces sound that is beyond the human audible frequency range.
What do you hear?What do you hear?
How are sound produced?
14.1 Nature and Production of Sound14.1 Nature and Production of Sound
�Sound is a form of that can passed from one point to another as a .
�Sound is a form of that can passed from one point to another as a .
energy
wave
14.1 Nature and Production of Sound14.1 Nature and Production of Sound
�All sound is produced by a source placed in a .
�Examples of vibrating sources include
.
�All sound is produced by a source placed in a .
�Examples of vibrating sources include
.
vibratingmedium
vibrating strings in piano or guitar, vibrating air column in flute or trumpet, vibrating membrane in a drum or vocal cord
How do Sound travels?How do Sound travels?
�The sound vibrations produce a series of and
of the particles in the surrounding medium.
�The sound vibrations produce a series of and
of the particles in the surrounding medium.
compressionrarefaction
How do sound travels?How do sound travels?
� Prongs are stationary.� Prongs are stationary.
no disturbance in air particles
How do sound travels?How do sound travels?
� Prongs move outwards. (pushes air particles)
� Prongs move outwards. (pushes air particles)
compression
{
How do sound travels?How do sound travels?
� Prongs move inwards. (pulls air particles)
� Prongs move inwards. (pulls air particles)
rarefaction
{
How do sound travels?How do sound travels?
� Prongs continuing to vibrate.� Prongs continuing to vibrate.
one wavelength
rarefaction(low pressure)
{
compression(high pressure)
{
compression(high pressure)
{
How do sound travels?How do sound travels?
�Compressions are places where the air pressure is than the surrounding air pressure.
�Rarefaction are places where the air pressure is than the surrounding air pressure.
�Compressions are places where the air pressure is than the surrounding air pressure.
�Rarefaction are places where the air pressure is than the surrounding air pressure.
higher
lower
How do sound travels?How do sound travels?
� By measuring air pressure at different points along the direction of travel of sound, the following pressure-distance graph can be obtained.
� By measuring air pressure at different points along the direction of travel of sound, the following pressure-distance graph can be obtained.
Air
Pressure
High
Low
Surrounding Air
Pressure
Amplitude
AmplitudeDistance
Compression Compression
Rarefaction Rarefaction
wavelength
How do sound travels?How do sound travels?
� The diagram below shows how the vibrating particles look like within the pipe where sound waves are travelling through:
� The diagram below shows how the vibrating particles look like within the pipe where sound waves are travelling through:
compression
rarefaction
The Bell-Jar ExperimentThe Bell-Jar Experiment
The Bell-jar ExperimentThe Bell-jar Experiment
The Bell-Jar ExperimentThe Bell-Jar Experiment
The Bell-jar ExperimentThe Bell-jar ExperimentStage 1:
The bell circuit is completed by closing the switch.
Seen and Heard:The movement of the strikercan be seen and the soundof the bell ringing can be heard.
Deduction:Sound is produced by vibrations.
The Bell-Jar ExperimentThe Bell-Jar Experiment
The Bell-jar ExperimentThe Bell-jar ExperimentStage 2:
The tap is closed and the vacuum pump is switched
on.
Seen and Heard:The movement of the strikercan be seen but the sound of the bell ringing gets fainter with time until it can no longer be heard.
The Bell-Jar ExperimentThe Bell-Jar Experiment
The Bell-jar ExperimentThe Bell-jar ExperimentStage 2:
The tap is closed and the vacuum pump is switched
on.
Deduction:Sound cannot travel through vacuum.
The Bell-Jar ExperimentThe Bell-Jar Experiment
The Bell-jar ExperimentThe Bell-jar ExperimentStage 3:
The vacuum pump is switched off and the tap is
open.
Seen and Heard:The movement of the strikercan be seen and the soundof the bell ringing can be heardagain.
The Bell-Jar ExperimentThe Bell-Jar Experiment
The Bell-jar ExperimentThe Bell-jar ExperimentStage 3:
The vacuum pump is switched off and the tap is
open.
Deduction:Sound requires a medium fortransmission.
The Bell-Jar ExperimentThe Bell-Jar Experiment
The Bell-jar ExperimentThe Bell-jar Experiment
Note:
� Bell should be not be touching
the bell-jar and the table and the
wire should also be kept thin.
� This is to prevent the sound
from traveling through them.
QuizQuiz
�Based on our discussions so far, what type of waves are sound waves, transverse or longitudinal? Why?
�Can sound waves be heard in outer space? Why?
�Based on our discussions so far, what type of waves are sound waves, transverse or longitudinal? Why?
�Can sound waves be heard in outer space? Why?
QuizQuiz
�Based on our discussions so far, what type of waves are sound waves, transverse or longitudinal? Why?
�Based on our discussions so far, what type of waves are sound waves, transverse or longitudinal? Why?
Sound wave is a longitudinal wave.
As the direction of vibration of particles is parallel to the wave motion.
QuizQuiz
�Can sound waves be heard in outer space? Why?
�Can sound waves be heard in outer space? Why?
No, as sound wave requires a medium to travel.
Speed of SoundSpeed of Sound
What can be deduced from the above data?
� Speed of light in air is than speed of sound in air.
� Speed of sound increases when the distance between the molecules in the medium .
�
What can be deduced from the above data?
� Speed of light in air is than speed of sound in air.
� Speed of sound increases when the distance between the molecules in the medium .
�
Speed of Light in air 300 000 000 m/s
Speed of Sound in air 330 m/s Speed of Sound in fresh water 1500 m/s
Speed of Sound in iron 5000 m/s
higher
decreases
Sound Wave EquationSound Wave Equation
�Since sound is a longitudinal wave, the wave equation also applies to sound.
Wave Equation
�Since sound is a longitudinal wave, the wave equation also applies to sound.
Wave Equation
v = f λ
Example 1Example 1
� A sound wave, of wavelength 600 mm and frequency of vibration 550 Hz, produces moving compressions and rarefactions in the air.
(a) Draw a sketch of how the sound waves look like, labeling regions of compression and rarefaction.
� A sound wave, of wavelength 600 mm and frequency of vibration 550 Hz, produces moving compressions and rarefactions in the air.
(a) Draw a sketch of how the sound waves look like, labeling regions of compression and rarefaction.
Example 1Example 1
� A sound wave, of wavelength 600 mm and frequency of vibration 550 Hz, produces moving compressions and rarefactions in the air.(b) From your sketch, what is the distance from the
middle of a compression to the middle of the nearest rarefaction in this wave at any instant?
� A sound wave, of wavelength 600 mm and frequency of vibration 550 Hz, produces moving compressions and rarefactions in the air.(b) From your sketch, what is the distance from the
middle of a compression to the middle of the nearest rarefaction in this wave at any instant?
Example 1Example 1
� A sound wave, of wavelength 600 mm and frequency of vibration 550 Hz, produces moving compressions and rarefactions in the air.
(c) How many compressions pass a point in one second?
� A sound wave, of wavelength 600 mm and frequency of vibration 550 Hz, produces moving compressions and rarefactions in the air.
(c) How many compressions pass a point in one second?
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
Pitch
� The “high” and “low” in music are known as .
� The pitch is related to of the sound waves.
Pitch
� The “high” and “low” in music are known as .
� The pitch is related to of the sound waves.
pitch
frequency
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
Pitch
� A high pitch note has a .
� A low pitch note has a .
Pitch
� A high pitch note has a .
� A low pitch note has a .
high frequency
low frequency
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
For String instruments
Factors affecting pitch of sound produced
� THICKNESS
� Thick string produces a .
� Thin string produces a .
For String instruments
Factors affecting pitch of sound produced
� THICKNESS
� Thick string produces a .
� Thin string produces a .
low pitch
high pitch
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
For String instruments
Factors affecting pitch of sound produced
� TENSION
� High tension string produces a .
� Low tension string produces a .
For String instruments
Factors affecting pitch of sound produced
� TENSION
� High tension string produces a .
� Low tension string produces a .low pitch
high pitch
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
For String instruments
Factors affecting pitch of sound produced
� LENGTH
� Long string produces a .
� Short string produces a .
For String instruments
Factors affecting pitch of sound produced
� LENGTH
� Long string produces a .
� Short string produces a .
low pitch
high pitch
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
For Wind instruments
Factors affecting pitch of sound produced
� LENGTH of column of air
� Short column of air produces a .
� Long column of air produces a .
For Wind instruments
Factors affecting pitch of sound produced
� LENGTH of column of air
� Short column of air produces a .
� Long column of air produces a .low pitch
high pitch
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
Waveform of different pitch sound.Waveform of different pitch sound.
Displacement
Time
Waveform of
high pitch
sound
Displacement
Time
Waveform of
low pitch sound
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
Loudness
� The loudness of the sound is related to of the waveform.
Loudness
� The loudness of the sound is related to of the waveform.amplitude
14.3 Pitch, Loudness and Quality14.3 Pitch, Loudness and Quality
Waveform of different loudness sound.Waveform of different loudness sound.
Displacement
Time
Waveform of
soft sound
Displacement
Time
Waveform of
loud sound
14.4 Application and Uses of Sound14.4 Application and Uses of Sound
�When a sound strikes a surface, part of the sound is reflected and the rest is absorbed. The sound reflected off hard, flat surfaces such as a large wall or a distance cliff is known as an
.
�When a sound strikes a surface, part of the sound is reflected and the rest is absorbed. The sound reflected off hard, flat surfaces such as a large wall or a distance cliff is known as an
.echo
14.4 Application and Uses of Sound14.4 Application and Uses of Sound
�Similarly to light, the reflection of sound follows the law of reflection as shown in the diagram below.
�Similarly to light, the reflection of sound follows the law of reflection as shown in the diagram below.
� Ships and animals (eg. Whales, dolphin, bats) use echo to
respectively.
� Ships and animals (eg. Whales, dolphin, bats) use echo to
respectively.
14.4 Application and Uses of Sound14.4 Application and Uses of Sound
find the depth of the sea, and their way around
� Echoes can be used to determine the between two locations. For
example, fishing ships use echoes to locate fish in the sea. This is called
� Echoes can be used to determine the between two locations. For
example, fishing ships use echoes to locate fish in the sea. This is called
14.4 Application and Uses of Sound14.4 Application and Uses of Sound
distance
echolation
Example 1Example 1� A person fires a gun at a distance away from
a cliff. He manage to hear the echo 2 s later. How far is he standing away from the cliff if the speed of sound in air is 330m/s.
� A person fires a gun at a distance away from a cliff. He manage to hear the echo 2 s later. How far is he standing away from the cliff if the speed of sound in air is 330m/s.
Example 2Example 2� The survivor of a shipwreck lands on an
island which is 3000 m from a vertical cliff. He sees a ship anchored between the island and the cliff. A blast from the ship’s horn is heard twice with a time lapse of 4 s. Assume that speed of sound = 330 m/s. Calculate the distance s of the ship from the island.
� The survivor of a shipwreck lands on an island which is 3000 m from a vertical cliff. He sees a ship anchored between the island and the cliff. A blast from the ship’s horn is heard twice with a time lapse of 4 s. Assume that speed of sound = 330 m/s. Calculate the distance s of the ship from the island.