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CHAPTER 12 MECHANICAL WAVES AND SOUND

CHAPTER 12 MECHANICAL WAVES AND SOUND. Goals for Chapter 12. To describe mechanical waves. To study superposition, standing waves and sound. To present sound as a standing longitudinal wave. To study sound intensity and beats. To examine applications of acoustics and musical tones.

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CHAPTER 12 MECHANICAL WAVES AND SOUND

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  1. CHAPTER 12 MECHANICAL WAVES AND SOUND

  2. Goals for Chapter 12 • To describe mechanical waves. • To study superposition, standing waves and sound. • To present sound as a standing longitudinal wave. • To study sound intensity and beats. • To examine applications of acoustics and musical tones.

  3. A disturbance that propagates from one place to another is referred to as a wave. Mechanical waves propagate with well-defined speeds determined by the properties of the material (medium) through which they travel. Waves carry energy, not matter.

  4. In a transverse wave individual particles move at right angles to the direction of wave propagation. In a longitudinal wave individual particles move in the same direction as the wave propagation.

  5. A wave on a string

  6. As a wave on a string moves horizontally, all points on the string vibrate in the vertical direction.

  7. Water waves from a disturbance.

  8. Wavelength, Frequency, and Speed

  9. vwave =λ /Tλ f = vwave Speed of a wave

  10. REFLECTIONS AND SUPERPOSITION

  11. A reflected wave pulse: fixed end

  12. A reflected wave pulse: free end

  13. The Principle of supperposition: • Whenever two waves overlap, the actual • displacement of any point on the string, • at any time, is obtained by vector addition • of the following two displacements: • The displacement the point would have • if ONLY the first wave were present • 2) The displacement the point would have • if ONLY the second wave were present

  14. Constructive Interference

  15. Destructive Interference

  16. Figure 14-22Interference with Two Sources

  17. Waves become coherent Depending on the shape and size of the medium transmitting the wave, different standing wave patterns are established as a function of energy.

  18. Normal modes for a linear resonator • The resonator is fixed at both ends. • Wave energy increases as you go down the y axis below.

  19. Fundamental frequencies • The fundamental frequency depends on the properties of the resonant medium. • If the resonator is a string, cord, or wire, the standing wave pattern is a function of tension, linear mass density, and length.

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