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Chapter 16 - Sound Waves

Speed of Sound Sound Characteristics Intensity Instruments: Strings and Pipes 2 Dimensional Interference Beats Doppler Effect Sonic Boom and shock waves. Chapter 16 - Sound Waves. Sound Speed. Variation with Temperature:. Air. Seawater. Pitch is frequency.

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Chapter 16 - Sound Waves

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  1. Speed of Sound Sound Characteristics Intensity Instruments: Strings and Pipes 2 Dimensional Interference Beats Doppler Effect Sonic Boom and shock waves Chapter 16 - Sound Waves

  2. Sound Speed Variation with Temperature: Air Seawater

  3. Pitch is frequency Middle C on the piano has a frequency of 262 Hz. What is the wavelength (in air)? 1.3 m

  4. Intensity of sound • Loudness – intensity of the wave. Energy transported by a wave per unit time across a unit area perpendicular to the energy flow.

  5. Sound Level - Decibel

  6. Stringed instruments

  7. Question 1 • A steel wire in a piano has a length of 0.9 m and a mass of 5.4 g. To what tension must this wire be stretched so that its fundamental vibration corresponds to middle C: i.e., the vibration possess a frequency 261.6.

  8. Wind instruments – Double open ended pipes Frequencies are identical to waves on a string

  9. Wind instruments – Single open ended pipes Only odd harmonics are present

  10. Question 2 – Pepsi Bottle • What is the fundamental frequency of a pepsi bottle 32 cm tall when you blow over it. Assume the speed of sound in air is 343 m/s. • 5 cm of water are added to the bottle. What is the new resonant frequency. 32 cm

  11. Waves on the surface of a liquid

  12. Two dimensional wave reflection

  13. Interference in Space When the path lengths from source to receiver differ by l/2 destructive interference results.

  14. Interference in Time - Beats • Two sounds of different frequency: • Superposition:

  15. Interference in Time - Beats • Trig identity again: Amplitude varies in time at a frequency equal to the difference in the two frequencies Beat Frequency

  16. Beats

  17. Doppler Effect

  18. Doppler Effect – 4 cases • Source moving toward receiver • Source moving away from receiver • Receiver (observer) moving towards source • Receiver (observer) moving away from source.

  19. Away: Source moving case Towards:

  20. Receiver (observer) moving case Towards: Away:

  21. Source and receiver moving • Numerator – Receiver (observer) • Toward + • Away – • Denominator – Source • Toward – • Away +

  22. Doppler Example • Intelligence tells you that a particular piece of machinery in the engine room of a Soviet Victor III submarine emits a frequency of 320 Hz. Your sonar operator hears the machinery but reports the frequency is 325 Hz. Assume you have slowed to a negligible speed in order to better hear the Russian. • Is the VIII coming toward you or moving away from you? • Assuming the Victor is either moving directly toward or away from you, what is his speed in m/s?

  23. Shock waves and the sonic boom

  24. Sometimes you hear 2 booms

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