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Ch. 15 Sound

Ch. 15 Sound. Milbank High School . Sec. 15.1 Properties of Sound. Objectives Demonstrate knowledge of the nature of sound waves and the properties sound shares with other waves. Solve problems relating the frequency, wavelength, and velocity of sound.

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Ch. 15 Sound

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  1. Ch. 15Sound Milbank High School

  2. Sec. 15.1Properties of Sound • Objectives • Demonstrate knowledge of the nature of sound waves and the properties sound shares with other waves. • Solve problems relating the frequency, wavelength, and velocity of sound. • Relate the physical properties of sound waves to the way we perceive sound. • Define the Doppler shift and identify some of its applications.

  3. Sound Waves • Are pressure variations that are transmitted through matter • Air molecules colliding • Longitudinal waves • Speed depends on air temperature • Warmer=faster

  4. Sound Waves • Can’t exist in a vacuum • Echoes • Reflected sound waves • Sonar

  5. Loudness • Depends on amplitude • We hear based upon pressure differences • Larger amplitudes create a higher pressure differences • Sound level • Decibels (dB) • 0 dB (most faintly heard), 2 x 10-5 Pa • Tenfold increase, 2 x 10-4 Pa is 20 dB • 110 is painful (most concerts)

  6. Pitch • Difference in frequency • Middle C: 262 Hz • E: 327 Hz • Human hearing • 20-16000 Hz • SIM – Pitch/Beat Freq • SIM – Pitch/Beating Freq

  7. Doppler Shift • Police siren as it drives by SIM • More sound waves reach you when the vehicle is moving towards you • Vehicle + waves = higher frequency • Waves – vehicle = lower frequency • Bats: • Insects flying away: lower frequency • Insects flying towards: higher frequency

  8. Sec. 15.2The Physics of Music • Objectives • Describe the origin of sound. • Demonstrate an understanding of resonance, especially as applied to air columns. • Explain why there is a variation among instruments and among voices using terms timbre, resonance, fundamental, and harmonic. • Determine why beats occur.

  9. Sources of Sound • Produced by vibrating objects • Vocal cords • Brass instruments • Reed instruments • Stringed Instruments • Others

  10. Resonance • When one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion. • Sometimes occurs in a column or tube (trombone) • Length of air column determines the frequency

  11. Closed pipe resonance • One closed end (marimba, pipe organ, sea shell) • First sound heard at ¼ wavelengths • Additional resonance lengths found at half-wavelength intervals

  12. Open-end Resonance • Woodwinds, brass • Sounds loudest at half-wavelengths • Wavelengths half as long as in a closed ended tube • Leads to twice the frequency

  13. Sound Quality • Fundamental • Lowest frequency • Harmonics • Odd-numbered multiples of the fundamental frequencies • Dissonance • Unpleasant set of pitches • Consonance • Pleasant set of pitches

  14. Musical intervals • Octave • Frequencies in a 1:2 ratio • Ex: 1st note-440 Hz, octave higher would be 880 Hz • Also corresponds to harmonics

  15. Beat Notes • Beat • Oscillation of wave amplitude • Beat frequency is the difference between the two frequencies

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