Transcript Sound - bYTEBoss

Sound
Name: ________________
Class: _________________
Index: ________________
Objectives
-- describe the production of sound by vibrating sources.
-- describe the longitudinal nature of sound waves and describe
compression and rarefaction and deduce that a medium is
required in order to transmit these waves.
-- the speed of sound differs in air, liquids and solids.
-- describe a direct method for the determination of the speed of
sound in air and make necessary calculation.
-- explain how the loudness and pitch of sound waves to amplitude
and frequency.
-- explain why different instruments produce sounds of different
quality.
-- 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, e.g. cleaning,
quality control and pre-natal scanning.
WAVE NATURE OF SOUND
•SOUND IS A FORM OF ENERGY THAT COMES IN THE
FORM OF LONGITUDINAL WAVES.
•SOUND IS PRODUCED BY ANY VIBRATING SOURCE
PLACED IN A MEDIUM.
LONGITUDINAL SOUND WAVES CONSISTS OF
COMPRESSIONS AND RAREFACTIONS.
THE DISTANCE BETWEEN TWO CONSECUTIVE
COMPRESSIONS AND RAREFACTIONS IS THE
WAVELENGTH OF THE SOUND WAVES.
Compression and Rarefactions
A tuning fork has a pure frequency
THE TRANSMISSION OF SOUND.
THE MECHANICAL NATURE OF SOUND.
•SOUND WAVES REQUIRE A MEDIUM FOR
TRANSMISSION.
•THE SPEED OF SOUND WAVES VARIES FROM ONE
MEDIUM TO ANOTHER. IT IS FASTEST IN SOLIDS,
NEXT IN LIQUIDS, AND SLOWEST IN GASES.
MEDIUM
AIR
APPROXIMATE SPEED / m/s
300
WATER
1500
IRON
5000
Changes in
Effect of sound in air
Temperature
As temperature increases, speed
increases.
Humidity
As humidity increases, speed increases
Pressure
Change in pressure has NO effect on
speed
An F/A-18F Super Hornet
hits the speed of sound. As
the plane pushes air away,
the temperature drops and
water vapor in the air
forms a ring cloud around
it.
THE HUMAN EAR.
AUDIBILITY
•THE RANGE OF FREQUENCIES WHICH A LISTENER CAN HEAR
IS KNOWN AS THE RANGE OF AUDIBILITY.
•FOR THE HUMAN EAR, THE LOWER LIMIT IS
APPROXIMATELY 20 HZ AND THE UPPER LIMIT 20 000HZ.
•OUR EARS CANNOT HEAR SOUND OF VERY HIGH
FREQUENCIES (ULTRASOUND) OR VERY LOW
FREQUENCIES (INFRASOUND).
Infrasound
Range of audibility
Ultrasound
Below 20 Hz
20 Hz – 20 000Hz
Above 20 kHz
Detectable by Dogs, Bats
Used in detection of mines in
the sea and foetuses in the
womb.
Ultrasound travels freely
through fluid and soft
tissues. However,
ultrasound is reflected
back (it bounces back as
'echoes') when it hits a
more solid (dense)
surface. For example, the
ultrasound will travel
freely though blood in a
heart chamber. But, when
it hits a solid valve, a lot
of the ultrasound echoes
back. Another example is
that when ultrasound
travels though bile in a
gallbladder it will echo
back strongly if it hits a
solid gallstone.
The unit for sound is the decibel.
Sound Level Meter
THE REFLECTION OF SOUND
•SOUND WAVES UNDERGO REFLECTION.
•AN ECHO IS A REFLECTION OF SOUND.
USES OF ECHOES INCLUDE;
•1. FINDING THE DEPTH OF THE SEA OR THE LOCATIONS OF
SHOALS OF FISH.
•2. DETECTION OF MINES.
•3. DETECTION OF OBSTACLES BY BATS.
Reflection of Sound
Multiple echoes are a nuisance
REVERBERATION IS THE EFFECT OF PROLONGED
SOUND DUE TO THE MERGING OF MANY ECHOS.
Sonar (originally an acronym for SOund Navigation And Ranging) is
a technique that uses sound propagation (usually underwater, as in
Submarine navigation) to navigate, communicate with or detect other
vessels. Two types of technology share the name "sonar": passive
sonar is essentially listening for the sound made by vessels; active
sonar is emitting pulses of sounds and listening for echoes.
Sonar may be used as a means of acoustic location and of
measurement of the echo characteristics of "targets" in the
water (i.e. fishes).
Example
A sound signal from the sonar on a ship is sent underwater into the
sea. It takes 1.35 s for the signal to return to the ship. If sound travels
at 1500 m/s, how deep is the sea?
Solution
Depth = 1500 m/s x (1.35/2) s
= 1012.5 m
= 1.01 x 103 m (3 s.f.)
MEASURING THE SPEED OF SOUND
Direct Method
MEASURING THE SPEED OF SOUND
Echo Method
•MUSICAL NOTES CAN BE DESCRIBED BY
•1. PITCH
•2. LOUDNESS
•3. QUALITY.
•WHEN WE DESCRIBE A MUSICAL NOTE OR SOUND AS
“HIGH” OR “LOW”, WE ARE COMMENTING ON THE PITCH
OF THE SOUND.
•PITCH IS RELATED TO THE QUANTITY CALLED
FREQUENCY.
•THE HIGHER THE FREQUENCY, THE HIGHER THE PITCH.
Pitch is related to the frequency of
sound
High pitch
Low pitch
•LOUDNESS IS RELATED TO THE QUANTITY OF
AMPLITUDE.
louder
softer
Question
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How do you change the
pitch in the guitar?
1. length of string
2. tension of string
3. cross-section of string
How do you change the
loudness in the guitar?
1. By plucking it harder.
Quality
THE SAME NOTE PLAYED ON
DIFFERENT MUSICAL INSTRUMENTS
SOUNDS DIFFERENT
ALTHOUGH THE FREQUENCY
AND AMPLITUDE ARE THE SAME.
i.e. Middle C on PIANO
Middle C on VIOLIN
Do they sound the same?
Differences in Quality of
Sound
Stringed instruments
sound different for many
reasons. What you hear
depends on how and of
what the string is made,
how the string is
vibrating, how long it
vibrates, and how long
you can hear it vibrate.
overtones
References
http://www.privateline.com/TelephoneHistory/soundwaves.html
http://www.worldculturepictorial.com/blog/comment/reply/574
http://en.wikipedia.org/wiki/Sonar
http://visual.merriam-webster.com/artsarchitecture/music/traditional-musical-instruments_7.php
http://www.hps.cam.ac.uk/whipple/explore/acoustics/historicalnotes
/
http://www.webweaver.nu/clipart/music/piano.shtml