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Chapter 19: Sound

Chapter 19: Sound. For those who have ears!. Decibels. 19.1 Properties of Sound. Interference. Longitudinal Waves. 343 m/s. Doppler Effect. PRESSURE VARIATIONS. ECHOES. 19.1 Objectives.

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Chapter 19: Sound

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  1. Chapter 19: Sound For those who have ears!

  2. Decibels 19.1 Properties of Sound Interference Longitudinal Waves 343 m/s Doppler Effect PRESSURE VARIATIONS ECHOES

  3. 19.1 Objectives Demonstrate knowledge of the nature of sound waves and the properties sound shares with other waves. Solveproblems relating the frequency, wavelength, and velocity of sound. Define the Doppler shift and identify some of the applications.

  4. What is Sound? What is sound? Sound is a form of energy, just like electricity and light. Sound is made when air molecules vibrate longitudinally and move in a pattern called waves, or sound waves. They are also referred to as compression or pressure waves. Think of when you clap your hands, or when you slam the car door shut. That action produces sound waves, which travel to your ears and then to your brain, which says, "I recognize that sound.” For humans, sound most commonly travels through the air. But it can travel through other mediums like water.

  5. What does it look like? Sound is invisible for the most part. It is heard not seen. There are fun toys that make big air bursts that you can feel But what does sound “look like”? Since sound needs a medium like air, it cannot travel in a vacuum.

  6. Visualizing Sound

  7. The Speed of Sound Since sound travels in the medium of air, its speed is fixed. It does however, vary with the temperature of air. At 0 C, the speed of sound is 331.451 m/s. At 20 C, the speed of sound is 343.371 m/s. At 40 C, the speed of sound is 354.891 m/s. As a rule of thumb, the speed of sound changes by about 12 m/s for every 20 C of temperature change. The most common value used is 343 m/s.

  8. Sound Measurement Sound amplitude is measured in decibels (dB). The decibel scale is a logarithmic scale. The sound amplitude is also called sound level or loudness. Table of sound levels dB Jet aircraft, 50 m away 140 Threshold of pain 130 Threshold of discomfort 120 Chainsaw, 1m distance 110 Disco, 1 m from speaker 100 Diesel truck, 10 m away 90 Kerbside of busy road, 5 m 80 Vacuum cleaner, distance 1 m 70 Conversational speech, 1m 60 Average home 50 Quiet library 40 Quiet bedroom at night 30 Background in TV studio 20 Rustling leaf 10 Threshold of hearing 0

  9. Spinal Tap: This one goes to 11…

  10. Sound Frequency Ranges Humans can hear from 20 hz to 20,000 Hz. Other animals have larger ranges. Species Approximate Range (Hz) human 64-23,000 dog 67-45,000 cat 45-64,000 cow 23-35,000 horse 55-33,500 sheep 100-30,000 rabbit 360-42,000 rat 200-76,000 mouse 1,000-91,000 gerbil 100-60,000 guinea pig 54-50,000 hedgehog 250-45,000 raccoon 100-40,000 ferret 16-44,000 opossum 500-64,000 Species Approximate Range (Hz) chinchilla 90-22,800 bat 2,000-110,000 beluga whale 1,000-123,000 elephant 16-12,000 porpoise 75-150,000 goldfish 20-3,000 catfish 50-4,000 tuna 50-1,100 bullfrog 100-3,000 tree frog 50-4,000 canary 250-8,000 parakeet 200-8,500 cockatiel 250-8,000 owl 200-12,000 chicken 125-2,000

  11. Sound Speed Sound Speed - The distance a sound travels in a given time. It is given as the frequency times the wavelength. If the frequency increases then the wavelength must decrease since the speed is constant.

  12. Speed of Sound in Other Media The speed of sound depends on the media the sound wave travels through.

  13. Echoes Reflected waves are called echoes and can be used to measure the distance from source to the object. This is how bats, who have poor eyesight and travel at night, navigate. Sound can also be diffracted. It can bend around barriers.

  14. Sonar Sonar is reflected sound waves (echoes) that travel through a water media rather than an air media.

  15. Doppler Effect

  16. Doppler Shift Doppler shift: If the sound source is coming towards you at a significant velocity, the sound pitch will get higher. If the sound source is moving away from you then the sound pitch is lowered. doppler motions

  17. Doppler Shift Doppler shift: If the sound source is coming towards you at a significant velocity, the sound pitch will get higher. If the sound source is moving away from you then the sound pitch is lowered. Doppler Demo

  18. 19.2 The Physics of Music

  19. 19.2 Objectives Describe the origin of sound. Demonstatean understanding of resonance, especially as applied to air columns. Explain why there is a variation among instruments and among voices using the terms timbre, resonance, fundamental, harmonic. Determine why beats occur.

  20. Concept Development Map Sound Vocabulary Definitions Re-sonance (again-sound). The act of resounding, being resonant Resonance Latin: sonus (sound) & sonans (to make a noise); a sound; a tune Sound vibrations are transferred to another object with the same natural frequency of vibration. The two agree. Related words: Sonic, sonar, sonant, sonata, sonation Sonance Quality or state of being sonant; sonancy Dissonance Dis-sonance (mismatched-sound). Sound vibrations that “fight” With each other. Discord, disharmony. Con-sonance (with-sound). The act of sounding together; Harmony (different frequency). Consonance

  21. Resonance Resonance - The tendency of a system to oscillate at maximum amplitude at certain frequencies, known as the system's resonance frequencies (or resonant frequencies). At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system stores vibrational energy. Closed Tube Open Tube

  22. 82 Resonance Demo

  23. 83 “Break Step” and Bridges

  24. Pitch and Timbre Pitch - The musician’s word for frequency of the sound. Timbre - The tone quality or color of the sound wave generated by the instrument. The extra distortions of the pure sine wave accounts for the unique sound of the human voice, and different instruments. Beat - An oscillation of wave amplitude caused by the sounding of two nearly identical frequencies. The superposition of the waves makes a slower moving wave.

  25. Timbre

  26. Consonance and Dissonance Consonance - A pleasant combination of pitches. Dissonance - A unpleasant combination of pitches. Can be described as “jarring”.

  27. Harmonics and Octaves Harmonics - Any higher frequency that is a multiple of the original frequency ( f ). Octave - Two frequencies in a 1:2 ratio.

  28. Mr. Mosher’s Band Trombone - A slide trombone lengthens the instrument’s tube by tube within a tube action. Guitar - Various frequencies, Harmonics, and Beats can all be demonstrated on the guitar. Throat - Please don’t ask Mr. Mosher to play his throat!

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