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 SOUNDSOUND 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.
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/sAIR 300WATER 1500IRON
9 As temperature increases, speed increases. Humidity Changes inEffect of sound in airTemperatureAs temperature increases, speed increases.HumidityAs humidity increases, speed increasesPressureChange in pressure has NO effect on speedAn 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).InfrasoundBelow 20 HzRange of audibility20 Hz – HzUltrasoundAbove 20 kHzDetectable by Dogs, BatsUsed 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.
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 ExampleA 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?SolutionDepth = 1500 m/s x (1.35/2) s= m= 1.01 x 103 m (3 s.f.)
21 MUSICAL NOTES CAN BE DESCRIBED BY 1. PITCH2. LOUDNESS3. 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 pitchLow pitch
23 LOUDNESS IS RELATED TO THE QUANTITY OF AMPLITUDE. loudersofter
24 Question How do you change the pitch in the guitar? 1. length of string2. tension of string3. cross-section of stringHow 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 ONDIFFERENT MUSICAL INSTRUMENTSSOUNDS DIFFERENTALTHOUGH THE FREQUENCYAND AMPLITUDE ARE THE SAME.i.e. Middle C on PIANOMiddle C on VIOLINDo 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.