1. MECHANICAL WAVES AND SOUND
CHAPTER 12
MECHANICAL WAVES AND SOUND

6. 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.

7. 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.

9. 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.

10. A wave on a string

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

12. Water waves from a disturbance.

13. Wavelength, Frequency, and Speed

15. Speed of a wave
vwave = λ /T λ f = vwave

16. REFLECTIONS AND SUPERPOSITION

17. A reflected wave pulse: fixed end

18. A reflected wave pulse: free end

19. 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

20. Constructive Interference

21. Destructive Interference

22. Figure 14-22 Interference with Two Sources

23. 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.

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

25. 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.