Chapter 15 The Nature of Sound What is Sound??? Sound is a Longitudinal Wave traveling through matter.

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<ul><li> Slide 1 </li> <li> Slide 2 </li> <li> Chapter 15 </li> <li> Slide 3 </li> <li> The Nature of Sound What is Sound??? Sound is a Longitudinal Wave traveling through matter. </li> <li> Slide 4 </li> <li> Longitudinal Waves Matter vibrates in the same direction as the wave travels. </li> <li> Slide 5 </li> <li> Slide 6 </li> <li> Longitudinal Waves Compression Rarefaction </li> <li> Slide 7 </li> <li> Slide 8 </li> <li> Sound from a Tuning Fork </li> <li> Slide 9 </li> <li> Speed of Sound Sound is transmitted through matter. The Velocity of Sound depends on the matter that carries it. </li> <li> Slide 10 </li> <li> Sound travels at a velocity of 332m/s in air at 0 C. Sound travels faster through warm air than through cold air. The velocity of sound increases about 0.6m/s for each degree in temperature. Sound travels much faster through liquids and solids than through gases. At 20 C sound travels at 344m/s. </li> <li> Slide 11 </li> <li> Comparing Media MediaSpeed of Sound Air at 0C331m/s Air at 20C343m/s Water at 25C1493m/s Sea Water at 25C1533m/s Iron at 25C5130m/s Rubber at 25C1550m/s </li> <li> Slide 12 </li> <li> Human Hearing Frequency of Sound 20 Hz to 20,000 Hz. Sound above 20,000 Hz - Ultrasonic Sound less than 20 Hz Subsonic (Infrasonic) </li> <li> Slide 13 </li> <li> Frequency is Pitch </li> <li> Slide 14 </li> <li> Detection of Pressure Waves </li> <li> Slide 15 </li> <li> Ear Drum </li> <li> Slide 16 </li> <li> Intensity and Loudness Intensity of Sound Depends on the amplitude of the wave. Loudness Describes a persons response to sound intensity. </li> <li> Slide 17 </li> <li> Loudness is measured in Decibels(dB) For every 10dB change the sound doubles!! 70dB is twice 60dB 80dB is four times 60dB </li> <li> Slide 18 </li> <li> Faintest Sound Heard0dB Whisper15dB Rustling Leaves20dB Purring Cat25dB Average Home50dB Vacuum Cleaner75dB Noisy Restaurant 80dB Power Mower100dB Chain Saw115dB ------Painful ------- 120dB Jet Plane Taking Off150dB </li> <li> Slide 19 </li> <li> Interference Constructive Interference Occurs when the compressions and rarefactions of two or more waves come together. Louder Sound </li> <li> Slide 20 </li> <li> Interference Destructive Interference Occurs when a compression of one wave arrives at the same time as a rarefaction of another wave. Quieter Sound </li> <li> Slide 21 </li> <li> Interference Beats The result of compressions and rarefactions of two slightly different frequencies reaching your ears together. Beats </li> <li> Slide 22 </li> <li> f 1 = 512Hz f 2 = 514Hz Beats = f 1 - f 2 Beats = 2Hz (beats/s) = 514Hz - 512Hz </li> <li> Slide 23 </li> <li> The Doppler Effect The change in wave frequency caused by the motion of the sound source or the motion of the observer. </li> <li> Slide 24 </li> <li> The Doppler Effect Shorter Wavelength Higher Frequency </li> <li> Slide 25 </li> <li> The Doppler Effect Longer Wavelength Lower Frequency </li> <li> Slide 26 </li> <li> Slide 27 </li> <li> Slide 28 </li> <li> Speed of Sound </li> <li> Slide 29 </li> <li> Greater than the Speed of Sound </li> <li> Slide 30 </li> <li> Homework #15-1 PP: 1-4 Page: 352 Section Review Page:355 Due: 3/12/03 </li> <li> Slide 31 </li> <li> Resonance A resonant frequency is a natural frequency of vibration determined by the physical parameters of the vibrating object. </li> <li> Slide 32 </li> <li> Harmonics Vibrations which occur at a particular frequency is known as a harmonic. </li> <li> Slide 33 </li> <li> First Harmonic The lowest possible frequency at which a string could vibrate to form a standing wave pattern is known as the fundamental frequency or the first harmonic. </li> <li> Slide 34 </li> <li> First Harmonic </li> <li> Slide 35 </li> <li> Second Harmonic </li> <li> Slide 36 </li> <li> Third Harmonic </li> <li> Slide 37 </li> <li> Resonance in Air Columns Closed Air Column = 4L L = 4 / 3 L = 4 / 5 L </li> <li> Slide 38 </li> <li> Resonance in Air Columns Open Air Column = 2L L = L = 2 / 3 L </li> <li> Slide 39 </li> <li> Example A tuning fork is placed above an open-pipe resonator in which the length can be changed. The loudest sound is heard at a length of 67cm and the next loudest was heard at 100.5cm. If the temperature of the air is 20C what is the frequency of the tuning fork? </li> <li> Slide 40 </li> <li> Example 67cm 100.5cm (100.5 - 67)= 33.5cm 33.5cm = 233.5cm = 67cm = </li> <li> Slide 41 </li> <li> Example = 67cm = 0.67m v@20C = 343m/s v = f f = v/ f = 512Hz f = 343m/s 0.67m </li> <li> Slide 42 </li> <li> Homework #15-2 PP: 5-9 Page: 362 Due: 3/17/03 </li> <li> Slide 43 </li> <li> Music to Your Ears A back and forth motion is set up in a string, resulting in a regular vibration. The vibration is called a standing wave the location of the crests and troughs are always in the same place. </li> <li> Slide 44 </li> <li> In a wind instrument, holes are opened and closed, changing the length of the vibrating column of air. This changes the size of the standing wave. </li> <li> Slide 45 </li> <li> Noise Sound with no regular pattern or definite pitch. </li> <li> Slide 46 </li> <li> Tone Quality The differences among sounds of the same pitch and loudness. </li> <li> Slide 47 </li> <li> Music Musical Sounds Based on a series of notes called a musical scale. </li> <li> Slide 48 </li> <li> The Sound Spectrum: Fundamental and Harmonics </li> <li> Slide 49 </li> <li> Open Air Column = 2L L = L = 2 / 3 L f 1 = v/ f 1 = v/2L f 2 = v/L f 2 = 2f 1 f 3 = v/ 2 / 3 L f 3 = 3f 1 </li> <li> Slide 50 </li> <li> Fundamental Frequency First Overtone Second Overtone Third Overtone 262Hz 524Hz 786Hz 1048Hz </li> <li> Slide 51 </li> <li> Closed Air Column = 4L L = 4 / 3 L = 4 / 5 L f 1 = v/4L f 2 = v/ 4 / 3 L f 2 = 3f 1 f 3 = v/ 4 / 5 L f 3 = 5f 1 </li> <li> Slide 52 </li> <li> Fundamental Frequency First Overtone Second Overtone Third Overtone 256Hz 768Hz 1280Hz 1792Hz </li> <li> Slide 53 </li> <li> Harmony Notes that sound pleasing together. The ratio of the frequencies of tones that are in harmony are small whole numbers. Notes that are one octave apart. Middle C and C 524/262 = 2/1 Notes E and C 330/262 = 5/4 </li> <li> Slide 54 </li> <li> Dissonance and Consonance Dissonance combination of pitches that sound unpleasant. Consonance combination of pitches that sound pleasant. </li> <li> Slide 55 </li> <li> Musical Intervals Octave: Two notes that have a ratio of 1:2. Example: 440Hz 880Hz one octave higher. 220Hz one octave lower. </li> <li> Slide 56 </li> <li> Interference Constructive Interference Occurs when the compressions and rarefactions of two or more waves come together. Louder Sound </li> <li> Slide 57 </li> <li> Interference Destructive Interference Occurs when a compression of one wave arrives at the same time as a rarefaction of another wave. Quieter Sound </li> <li> Slide 58 </li> <li> Interference Beats The result of compressions and rarefactions of two slightly different frequencies reaching your ears together. Beats </li> <li> Slide 59 </li> <li> f 1 = 512Hz f 2 = 514Hz Beats = f 1 - f 2 Beats = 2Hz (beats/s) = 514Hz - 512Hz </li> <li> Slide 60 </li> <li> Homework #15-3 Practice Problem:10 Section Review Page: 367 Due: 3/18/03 </li> <li> Slide 61 </li> <li> Homework #15-4 Study Guide Due: 3/19/03 Test: 3/20/03 </li> </ul>

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