1. FOCUS 2 - FEATURES OF THE WAVE MODEL CAN BE USED TO ACCOUNT FOR THE PROPERTIES OF SOUND 8.2 The World Communicates

2. Sound Waves Sound waves are vibrations or oscillations of particles in a medium. The particles in a sound wave oscillate at the same frequency as the source. Sound waves can not travel through a vacuum. 13. Identify that sound waves are vibrations or oscillations of particles in a medium

3. Sound waves require a medium to travel through In Space no one can hear you scream! The speed of sound waves depends on the medium.  Speed of sound in  Air = 331 ms -1  Water (25 o C) = 1498 ms -1  Glass = 5640 ms -1  Aluminium = 6420 ms -1  Speed increases as the density of the medium increases. 13. Identify that sound waves are vibrations or oscillations of particles in a medium

4. Cathode Ray Oscilloscopes (CRO’s) An oscilloscope is a laboratory instrument commonly used to display and analyse the waveform of electronic signals. The sound to be analysed is played into a microphone which converts the sound waves into an electrical signal with the same properties as the wave. This signal is displayed on the screen. 14. perform a first-hand investigation and gather information to analyse sound waves from a variety of sources using the Cathode Ray Oscilloscope (CRO) or an alternate computer technology

5. Representing Sound waves... 15. relate compressions and rarefactions of sound waves to the crests and troughs of transverse waves used to represent them

6. Pitch and Volume of Sounds As frequency increases the pitch of a sound increases. As the amplitude increases the volume of the sound increases. Q. Which sound below has the:  highest pitch?  highest volume? 16. explain qualitatively that pitch is related to frequency and volume to amplitude of sound waves

7. Echoes Echoes are reflections of sound waves Used by some animals in echolocation Used in SONAR and Ultrasound 17. explain an echo as a reflection of a sound wave

8. Echoes Using echoes to find the distance to objects. For the diagram to the left it takes 5 seconds for the sound waves to travel to the object, be reflected and received back at the source. The speed of sound in air is 330 ms -1 Using Distance = 1650 m But this is the total distance the wave travels (ie. Up and back) So the distance to the object is 825m 17. explain an echo as a reflection of a sound wave Time = 5 seconds Distance = 1650 m Distance = 825 m

9. Echo Point – Blue Mountains A physics tourist attraction! 17. explain an echo as a reflection of a sound wave

10. Principle of Superposition “At any point where two waves overlap or meet, the total disturbance is the sum of the individual disturbances caused by the waves at that point.” http://www.surendranath.org/Applets.html 18. describe the principle of superposition and compare the resulting waves to the original waves in sound

11. Constructive Interference Constructive interference results in an increase in amplitude. 18. describe the principle of superposition and compare the resulting waves to the original waves in sound

12. Destructive Interference Destructive interference results in a decreased amplitude, or the waves may even cancel each other out. 18. describe the principle of superposition and compare the resulting waves to the original waves in sound