2. Sound Waves Sound Waves What Causes Sound? VIBRATIONS

3. Sound Waves Molecules in the air vibrate about some average position creating the compressions and rarefactions. We call the frequency of sound the pitch.

4. Longitudinal Waves vs. Transverse –Longitudinal waves follow the same “rules” as the transverse waves we have dealt with previously. –However, because cohesive forces between particle are necessary for transverse wave propagation, transverse waves only travel on the surface of fluids. –Where as, longitudinal waves may propagate through the “bulk” of a fluid, because they rely on pressure forces, not cohesive forces. (Pressure Gun DEMO)

5. The Fundamentals of Sound Waves Frequency Frequency –number of oscillations in pressure per second Wavelength Wavelength –distance between each successive region of high or low pressure. Sound waves are longitudinal waves

6. The Speed of Sound Molecules of the medium collide, allowing the wave to be transmitted through it. Molecules of the medium collide, allowing the wave to be transmitted through it. –The speed of sound depends on elasticity of the medium. –The more elastic the medium, the faster the sound. –Elasticity – the ability of a solid to return to its original shape after external forces have been exerted on it. Elasticity

7. The Medium What if there is no medium? What if there is no medium? –A vacuum perhaps… vacuum Waves in different media Waves in different media –In what medium will sound travel fastest… Steel, wood, or you? What does the speed of sound depend upon? The Medium

8. Visualizing Sound Ruben’s Tube Ruben’s Tube

9. Echo Location and Sonar

10. Loudness Loudness - depends on the amplitude of sound wave Loudness - depends on the amplitude of sound wave –Again, the amplitude of a wave indicates its energy. The greater the amplitude, the greater the energy. (DB Mic. DEMO) On the graphs to the right Where is the sound loudest?

11. Sound Levels Loudness is measured in Decibels (dB) (Data Table on page 477 of text) –Breathing 10 dB –Normal Speech 60 dB –Concert 115dB –Pain Threshold 120 dB.

12. Sound and Pitch Pitch - the frequency of a sound wave Pitch - the frequency of a sound wave –The human ear is not equally sensitive to all frequencies (EAR VISUAL & discussion) human ear human ear Most people cannot hear frequencies below 20Hz or above 16,000Hz (Audible ʄ DEMO ) Most people cannot hear frequencies below 20Hz or above 16,000Hz (Audible ʄ DEMO ) 20Hz or above 16,000Hz 20Hz or above 16,000Hz Most people are most sensitive to frequencies between 1,000 and 5,000 Hz Most people are most sensitive to frequencies between 1,000 and 5,000 Hz Musical Scale Example “middle C” has a frequency of 262 Hz. Example “middle C” has a frequency of 262 Hz.

13. Natural Frequency & Resonance Natural frequency (Singing Rod DEMO) Natural frequency (Singing Rod DEMO) –An object’s own set of frequencies –Depends primarily on elasticity and shape vs

14. Resonance When the frequency of a forced vibration matches the an object’s natural frequency, a dramatic increase in amplitude occurs (PVC Fisher Burner Demo)

15. Tacoma Narrows Bridge Unfortunately, resonance is not always a good thing… Unfortunately, resonance is not always a good thing…

16. Noise & Noise Reduction Noise Noise –sound of any kind (especially unintelligible or dissonant sound) Noise Reduction Noise Reduction Noise Reduction Noise Reduction –LORD Corporation – Aerospace Engineering –The use of destructive interference to eliminate noise

17. Doppler Effect Doppler Shift - Change in sound frequency due to the relative motion of either the source or the detector. Doppler Shift - Change in sound frequency due to the relative motion of either the source or the detector. example: a passing car example: a passing car

18. DOPPLER EFFECT Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves Doppler with Sound Doppler with Sound

19. Sonic BOOM Sonic BOOM An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the water waves caused by a ship's bow. An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the water waves caused by a ship's bow. When the aircraft exceeds the speed of sound, these pressure waves combine and form visible shock waves  When the aircraft exceeds the speed of sound, these pressure waves combine and form visible shock waves 

20. Subsonic - slower than the speed of sound Supersonic - Faster than the speed of sound Sub & Super Sonic Mach Number = speed of sound speed of object

21. Bow waves V-shaped pattern made by overlapping crest V-shaped pattern made by overlapping crest

22. Produced by supersonic aircraft, three-dimensional cone shaped Produced by supersonic aircraft, three-dimensional cone shaped Sonic boom – sharp crack heard when conical shell of compressed air that sweeps behind a supersonic aircraft reaches listeners on the ground below. Sonic boom – sharp crack heard when conical shell of compressed air that sweeps behind a supersonic aircraft reaches listeners on the ground below.Sonic boom Sonic boom Shock Waves

23. The Physics of Music What is the source of sound, again? What is the source of sound, again?VIBRATIONS The 3 Types of Musical instruments The 3 Types of Musical instruments All create Vibrations in air TypeOrigin TypeOrigin StringPlucked String StringPlucked String Wind Mouthpiece or Reed Wind Mouthpiece or Reed PercussionStretched Membrane PercussionStretched Membrane

24. For the Music Folks! Sound Quality Fundamental and Harmonics Fundamental and Harmonics Dissonance and Consonance Dissonance and Consonance Intervals and Octave Intervals and Octave –Beat Notes (DEMO) Beat –Superposition of waves Demo