13 nature of-sound

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  • Compressions The close together part of the waveRarefactions The spread-out parts of a wave
  • 1831 collapse of the Broughton Suspension Bridge and the 1850 collapse of Angers Bridge
  • 13 nature of-sound

    1. 1. The Nature of Sound
    2. 2. What is Sound? In human experience: That which we hear. In Physics: Oscillation of pressure transmitted through a medium at frequencies between 20Hz and 20 kHz.
    3. 3. Sound travels in longitudinal waves — vibrating compressions and rarefactions through air
    4. 4. Forced Vibrations setting up of vibrations in an object by a vibrating force
    5. 5. Natural Frequency The frequency at which an object tends to vibrate when hit, struck, plucked, strummed or somehow disturbed. Depends on – elasticity – shape
    6. 6. Harmonic frequencies are multiples of the fundamental natural frequency.
    7. 7. Resonance occurs whenever successive impulses are applied to a vibrating object in rhythm with its natural frequency.
    8. 8. Mechanical Resonance Following the collapse several bridges led to notices being placed warning troops to break step when crossing the bridge.
    9. 9. Shake-table crash testing of a building model.
    10. 10. Interference combined effect of two or more overlapping waves
    11. 11. Waves overlap crest-to- crest, resulting in a wave of increased amplitude.
    12. 12. Waves overlap trough-to- crest, resulting in a wave of decreased amplitude.
    13. 13. Destructive interference is the principle behind active noise-cancelling technology.
    14. 14. Beats are periodic variations in the loudness of sound due to interference.
    15. 15. Standing waves
    16. 16. This standing wave is a sum of two waves travelling in opposite directions.
    17. 17. Nodes of standing wave
    18. 18. Reflection
    19. 19. Sound waves refract when air near the ground is warmer than air above. Refraction
    20. 20. Interference combined effect of two or more overlapping waves
    21. 21. Beats are periodic variations in the loudness of sound due to interference.
    22. 22. Doppler Effect the change in frequency as measured by an observer due to the motion of the source or listener. Named after Austrian physicist and mathematician, Christian Johann Doppler
    23. 23. Water Bug Doppler Effect Top view of water waves made by a stationary bug jiggling (up and down) in still water. Water waves made by a bug swimming in still water toward point B. A & B receive different wave frequencies.
    24. 24. Doppler Effect Example of Doppler Effect: Frequency of waves received by an observer increases as a sound source approaches. Wave frequency decreases as the source recedes.
    25. 25. Stages of Wave Speeds Bug swims at successively greater speeds. Overlapping at the edges occurs only when the bug swims faster than wave speed.
    26. 26. Shock Waves and the Sonic Boom Shock wave pattern of overlapping spheres that form a cone from objects traveling faster than the speed of sound
    27. 27. Shockwave The shockwave actually consists of two cones. – A high pressure cone with its apex at the bow – A low pressure cone with its apex at the tail. – A graph of the air pressure at ground level between the cone takes the shape of the letter N.
    28. 28. Shockwave The shock wave has not yet reached listener A, but it is now reaching listener B, and it has already reached listener C.
    29. 29. Musical Sound Graphical representations of noise and music. (a) Noise has no clear repeatable pattern. (b) Music has a frequency (repeatable wave), wavelength, and speed.
    30. 30. Music and Standing Waves Each harmonic of a guitar string is a standing wave. Image shows the first four harmonics on the string.
    31. 31. Variations in Tone Images of a piano and clarinet playing note C Each has the same frequency, but with different extra vibrations. These differences produce tone.
    32. 32. end

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