Sound
1. What is Sound?
2. Transmission of Sound 3. Reflection of Sound 4. Ultrasound
5. Pitch and Loudness
Lesson Objectives
• 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
What is Sound?
•
Sound is a form of energy.
How Is Sound Produced?
• Sound is produced by vibrations and requires a medium for its propagation.
Motion of particles
Direction of sound propagation
Compression Rarefaction
Example: Vibrating object in air.
Sound in air consists of a series of compressions and
How Is Sound Produced?
Sound in air consists of a series of compressions and rarefactions moving away from the source of vibration.
When the speaker cone vibrates, it moves forward and backwards. • Move forward : Compresses the air particles in front of it.
Pressure-Distance Graph
• Compressions are regions of high pressure.
Wavelength
From the graph,
1.The distance between two consecutive compressions or rarefactions is the wavelength λ of the sound wave.
Displacement-Time Graph
Particle at rest/centre position A Particle returned to rest/centre position C Particle returned to rest/centre position E Particle moved to right B Particle moved to left D A BC D E
Transmission of Sound
Transmission of Sound
• Sound cannot travel through vacuum. (It requires a medium in order to travel from one point to another)
Medium of Transmission
•
Any medium which has particles that can vibrate
will
transmit sound.
Medium of transmission
•
Sound travels fastest
in solid
and slowest
in gas.
•
Sound energy is transmitted when particles transfers
energy to one another.
•
The energy transmitted will be faster
when the
particles are closer
to each other.
Transmission of sound in air
•
The speed of sound in air is about 330ms
-1,
Temperature
When temperature increases, molecules will move
about faster
and hence energy is
transferred faster
.
Humidity
When the level of
humidity increases, the
number
of particles increases.
When the number of particles
increases, the
distance between each particle is reduced.
Measuring the Speed of Sound In Air
Equipment needed:
•
Starting pistol
•
Stopwatch
Measuring the Speed of Sound In Air
Procedure:
1.
Observers A and B are positioned at a known
distance ,
d
, apart. (measured using measuring tape)
2.
Observer A fires the pistol.
Measuring the Speed of Sound In Air
Medium = Air
Speed of sound in air =
Distance travelled by sound, d Time taken, tPrecautions
Lesson Objectives
• Describe how the reflection of sound may produce an echo, and how this may be used for measuring distances
• Define ultrasound and describe one use of ultrasound
Reflection of Sound
• Sound can be reflected.
• An echo is a reflection of sound, arriving at the listener some time after the direct sound.
http://www.mybeijingchina.com/temple-of-heaven/echo_wall.htm
Echo Wall of Temple of Heaven
If one person speaks or even whispers at one side of it,
Reflection of Sound
How Are Echoes Formed?
• An echo is formed when a sound is reflected off hard, flat surfaces.
Surround sound system in concert halls
At a live performance, much of the sound you hear is reflected off the walls, ceiling and floor.
Only a small percentage
Uses of Echos
• To detect and locate objects (echolocation)
▫Used by bat to detect prey or find directions
▫Determine the position of submarines or shoals of fishes
Example 1
Fahmi stands some distance away from a cliff. He lets out a shout and hears his echo 4 s later. How far away is he from the cliff? (Take the speed of sound in air to be 330 ms-1)
Time taken for sound to travel from man to cliff and back to man = 4 s
Total distance travelled = 2d
Speed = total distance total time
= 2d 4
Example 2
An echo sent vertically downwards from a submarine is reflected from the ocean floor. The echo is detected by on submarine 5 s after transmission. If the speed of the echo in water is 1600 ms-1, what is the depth of the ocean floor?
Speed of echo in water = 1600ms-1
Total time taken = 5 s
Speed = total distance total time = 2d
5
1600
Total distance = 2d
Junhao stands in between two cliffs as shown in the diagram and fires his pistol. He heard two echoes. He heard the first echo after 2 s and the second echo after 5 s. Assuming that the speed of sound in air is 330 ms-1, find out what are the distances x and y.
Speed of sound in air= 330ms-1
Total time taken for 1st echo = 2 s
Total distance travelled for 1st echo = 2x
Speed = total distance total time = 2x
2
330
Therefore x = 330 m
Total time taken for 2nd echo = 5 s
Total distance travelled for 2nd echo = 2y
Speed = total distance total time = 2y
5
330
What sounds are audible?
• Audible means ‘to be able to be heard’.
• Our human ear cannot detect sounds of all frequencies.
• The range of audibility is the range of frequencies which a person can hear.
Infrasound
• Infrasound are sound with frequencies below the lower limit of human range of audibility.
• In general, infrasound is classified as sound with very low
Ultrasound
• Ultrasound are sound with frequencies above the upper limit of human range of audibility.
Applications Of Ultrasound
• Used in quality control of materials
Applications Of Ultrasound
• Used to obtain images inside body - commonly used to examine the development of a foetus.
• The ultrasound pulses are sent into the body using a
Lesson Objectives
• Relate loudness of a sound wave to its amplitude and pitch to its frequency
What distinguishes one sound from another?
Characteristics of Sound
• Pitch
• Loudness
Pitch
•
Pitch is related to the frequency
of a sound wave.
•
Frequency determines the pitch of sound
▫
Sound with higher
frequency have higher
pitch.
▫
Sound with lower
frequency have lower
pitch.
Lower frequency, lower pitch
higher frequency, higher pitch
Loudness
The loudness
of sound is dependent on the amount
of energy which is transferred to the medium.
It in turn is dependent on the amplitude
of
vibrations
of the object.
▫
Sound with larger
amplitude are louder.
▫
Sound with smaller
amplitude are softer.
Louder sound Harder you hit the
membrane
(More energy transfer)
Loudness
Loudness depends on the amplitude of the vibration.
Smaller amplitude,
Softer sound
Extra Notes : Timbre
• Timbre is the characteristic of sound describes the quality of the sound
Waveform of a Soprano singing the same pitch Waveform of a piano being
Lesson Closure
Sound Cannot travel through Longitudinal waves vibrations Loudness Pitch Echo Vacuum
•Travels fastest in solids. •Travels slowest in gas.
Used In Related to •Used to detect
development of foetus
Medium
Requires a
Can be reflected
Is characterized by
Frequency Related to Amplitude •Higher frequency, higher pitch •Lower frequency, lower pitch •Larger amplitude, louder sound •Smaller amplitude, softer sound Echolocation
•To detect and locate objects
Ultrasound Infrasound
Compressions
Rarefactions
Consists of Below this limit Above this limit
20 Hz 20 kHz Longitudinal
Soft Loud
Loudness
Pitch depends on frequency
Low High
References
•http://www.ndt-ed.org/EducationResources/HighSchool/Sound/reflection.htm
• http://www.youtube.com/watch?v=coWg_-1K4_A&feature=related
• http://www.youtube.com/watch?v=6HM_1qYpQrI
• http://womensobgynoframapo.com/yahoo_site_admin/assets/images/BA BY20RUB20EYE1.30173937_std.JPG
References
•
Glass Breaking
•
http://www.youtube.com/watch?v=6Es5nQdTbiA
•
http://www.youtube.com/watch?v=IZD8ffPwXRo&feature
=related
•
http://www.teachersdomain.org/resource/lsps07.sci.phys
