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Waves and Sound

Waves and Sound. PHYS 1090 Unit 7. crest. l. l. trough. Features of a Wave. Crest: high point . Trough: low point. Wavelength: crest-crest distance (m). Period: crest-crest-timing (s). u. A. Features of a Wave. Amplitude A : (crest height – trough height) / 2.

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Waves and Sound

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  1. Waves and Sound PHYS 1090 Unit 7

  2. crest l l trough Features of a Wave • Crest: high point • Trough: low point • Wavelength: crest-crest distance (m) • Period: crest-crest-timing (s)

  3. u A Features of a Wave • AmplitudeA: (crest height – trough height) / 2 • Frequencyf: repeats in a given time (cyc/s = Hz) • Velocityu: speed of crest motion (m/s)

  4. Relations between Features • Period T = 1 / f; Frequency f = 1 / T • Velocity u = l / T = lf • Wavelengthl=uT=u / f • Frequencyf = u / l; Period T = l / u

  5. Types of Waves • Motion of the medium is perpendicular to the direction the wave travels: transverse wave (example: string wave) • Motion of the medium is parallel to the direction the wave travels: longitudinal wave (examples: sound wave, slinky wave) • Animation

  6. Combining Waves

  7. result Adding Waves Together 3 0 –3

  8. Wave Interference • Constructive: Sum of waves has increased amplitude • Destructive: Sum of waves has decreased amplitude • Two-wave simulation

  9. Beats • Waves of similar frequency combine to give alternating times of constructive and destructive interference

  10. Standing Waves • Add a wave to an identical wave traveling in the opposite direction • (Its reflection) • Medium vibrates, but waves don’t travel • Nodes: positions of zero variation • Antinodes: positions of maximum variation

  11. Two-Dimensional Waves • Ocean waves, earthquake surface waves • Wave types animations • Membrane standing waves animations

  12. Water Waves • Restoring force is gravity • Fastest in deep water, slow in shallow water • Breaking and refractive behavior in shallow water • Speed depends on wavelength • Very complicated behavior!

  13. Shoaling and Breaking • Waves slow in shallows by shore • Wavelength shortens and amplitude rises • Troughs move slower than crests • Crests fall forward

  14. Wave refraction u = 1/2 u = 3/4 u = 1

  15. Ocean Wave Refraction

  16. 2-D Wave Interference • interference patterns • http://www.falstad.com/ripple/

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