chapter 14 - soundjyssphysic.weebly.com/uploads/4/5/0/5/45055149/chapter_14_-_soun… · chapter 14...

Chapter 14 - SoundChapter 14 - Sound

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.



� 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


� Prongs move outwards. (pushes air particles)

� Prongs move outwards. (pushes air particles)

compression

{


� Prongs move inwards. (pulls air particles)

� Prongs move inwards. (pulls air particles)

rarefaction

{


� Prongs continuing to vibrate.� Prongs continuing to vibrate.

one wavelength

rarefaction(low pressure)

{

compression(high pressure)

{

compression(high 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.

�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


� 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


� 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 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 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 tap is closed and the vacuum pump is switched

on.

Deduction:Sound cannot travel through vacuum.



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 vacuum pump is switched off and the tap is

open.

Deduction:Sound requires a medium fortransmission.


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?



QuizQuiz



Sound wave is a longitudinal wave.

As the direction of vibration of particles is parallel to the wave motion.

QuizQuiz



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) 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


(c) How many compressions pass a point in one second?


(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


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


For String instruments

Factors affecting pitch of sound produced

� THICKNESS

� Thick string produces a .

� Thin string produces a .



� THICKNESS

� Thick string produces a .

� Thin string produces a .

low pitch

high pitch




� TENSION

� High tension string produces a .

� Low tension string produces a .



� TENSION

� High tension string produces a .

� Low tension string produces a .low pitch

high pitch




� LENGTH

� Long string produces a .

� Short string produces a .



� LENGTH

� Long string produces a .

� Short string produces a .

low pitch

high pitch


For Wind instruments


� LENGTH of column of air

� Short column of air produces a .

� Long column of air produces a .

For Wind instruments


� LENGTH of column of air

� Short column of air produces a .

� Long column of air produces a .low pitch

high pitch


Waveform of different pitch sound.Waveform of different pitch sound.

Displacement

Time

Waveform of

high pitch

sound

Displacement

Time

Waveform of

low pitch sound


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


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


�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.


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


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.

chapter 14 - soundjyssphysic.weebly.com/uploads/4/5/0/5/45055149/chapter_14_-_soun… · chapter 14...

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