1. Sound Name: ________________ Class: _________________
Index: ________________

2. 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.

3. 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.

4. LONGITUDINAL SOUND WAVES CONSISTS OF COMPRESSIONS AND RAREFACTIONS.
THE DISTANCE BETWEEN TWO CONSECUTIVE COMPRESSIONS AND RAREFACTIONS IS THE WAVELENGTH OF THE SOUND WAVES.

6. Compression and Rarefactions

7. A tuning fork has a pure frequency

8. 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 APPROXIMATE SPEED / m/s
AIR 300
WATER 1500
IRON

9. As temperature increases, speed increases. Humidity
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.

10. 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 HZ.
OUR EARS CANNOT HEAR SOUND OF VERY HIGH FREQUENCIES (ULTRASOUND) OR VERY LOW FREQUENCIES (INFRASOUND).
Infrasound
Below 20 Hz
Range of audibility
20 Hz – Hz
Ultrasound
Above 20 kHz
Detectable by Dogs, Bats
Used in detection of mines in the sea and foetuses in the womb.

11. Ultrasound travels freely through fluid and soft tissues
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.

12. The unit for sound is the decibel.
Sound Level Meter

13. 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.

14. Reflection of Sound

15. Multiple echoes are a nuisance
REVERBERATION IS THE EFFECT OF PROLONGED SOUND DUE TO THE MERGING OF MANY ECHOS.

16. 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.

17. 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).

18. 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
= m
= 1.01 x 103 m (3 s.f.)

19. MEASURING THE SPEED OF SOUND
Direct Method

20. MEASURING THE SPEED OF SOUND
Echo Method

21. 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.

22. Pitch is related to the frequency of sound
High pitch
Low pitch

23. LOUDNESS IS RELATED TO THE QUANTITY OF AMPLITUDE.
louder
softer

24. Question 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.

25. Quality i.e. Middle C on PIANO Middle C on VIOLIN
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?

26. 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.

27. overtones

28. References