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 RarefactionsCompression and Rarefactions

A tuning fork has a pure frequencyA tuning fork has a pure frequency

THE TRANSMISSION OF SOUND.

THE MECHANICAL NATURE 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 APPROXIMATE SPEED / m/sAIR 300

WATER 1500

IRON 5000

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.

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

THE HUMAN EAR.AUDIBILITYAUDIBILITY•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

Below 20 Hz

Range of audibility

20 Hz – 20 000Hz

Ultrasound

Above 20 kHz

Detectable by Dogs, BatsUsed 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.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 Pitch is related to the frequency of soundsound

High pitch

Low pitch

•LOUDNESS IS RELATED TO THE QUANTITY OF AMPLITUDE.

louder

softer

QuestionQuestion

How do you change the How do you change the pitch in the guitar?pitch in the guitar?

1. length of string1. length of string 2. tension of string2. tension of string 3. cross-section of string3. cross-section of string How do you change the How do you change the

loudness in the guitar?loudness in the guitar? 1. By plucking it harder.1. By plucking it harder.

QualityQuality

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/arts-architecture/music/traditional-musical-instruments_7.php

http://www.hps.cam.ac.uk/whipple/explore/acoustics/historicalnotes/

http://www.webweaver.nu/clipart/music/piano.shtml