1. Chapter 17 – Mechanical Waves and Sound

2. 17.1 Mechanical Waves Water waves have two features common to all waves: 1. A wave is a traveling disturbance 2. A wave carries energy from place to place

3. 17.1 Mechanical Waves Mechanical Wave – a disturbance in matter that carries energy from one place to another Mechanical waves require matter to travel through. Medium – the material through which a wave travels A mechanical wave is created when a source of energy causes a vibration to travel through a medium Vibration – a repeating back and forth motion

4. 17.1 Mechanical Waves Each particle of a wave merely oscillates about an equilibrium point (no bulk flow of water) The wave moves but it does not carry matter with it (it travels through a medium)

5. 17.1 Mechanical Waves A single wave pulse shows that it is begun with a vibration and transmitted through internal forces in the medium.

6. 17.1 Mechanical Waves If the wave moves up and down at the same rate, a periodic wave is generated (note point P)

7. 17.1 Mechanical Waves Transverse Wave A transverse wave is one in which the disturbance is perpendicular to the direction of travel of the wave

8. 17.1 Mechanical Waves

12. Longitudinal Wave A longitudinal wave is one in which the disturbance is parallel to the line of travel of the wave Sound waves are longitudinal waves Rarefaction 17.1 Mechanical Waves

16. Rarefaction 17.1 Mechanical Waves

18. Which parts of a longitudinal wave correspond to the troughs and crests of a transverse wave? Assuming that the waves pictured are moving at the same speed, what is the relationship of their frequencies? What is the relationship between the direction a wavelength is measured and the direction the amplitude is measured for each wave pictured? As pictured, are these waves in phase or out of phase?

19. Surface Wave A wave that travels along a surface separating two media The combination of transverse and longitudinal movement results in a circular motion The bobber will not get closer to shore, but continue moving in a circle 17.1 Mechanical Waves

21. 17.2 Properties of Mechanical Waves Cycle – a wave is a series of many cycles (a complete vibration) Amplitude Wavelength (λ) – horizontal length of one cycle. The distance between successive crests, troughs, or any two successive points. crest trough

22. Period (T) – The time required for one complete up/down cycle (vibration). The time to travel one wavelength. Frequency (Hz) f = 1 __ T period and frequency depend only on the source of the wave, NOT on the speed or medium 17.2 Properties of Mechanical Waves

23. A simple relation exists between period, wavelength, and the speed of a wave. v = λ __ T = fλ v = f λ Speed of a Wave

24. The waves in a pool have a wavelength of 0.20 m and a frequency of 2.8 Hz. What is the speed of these waves? Example 1 A student moves the end of a soft spring back and forth to make waves. The waves travel at 1.8 m/s and have a wavelength of 1.2 m. What is the frequency of these waves? Example 2 Page 506 Math Skills and Math Practice 17.2 Properties of Mechanical Waves

25. Often, two or more waves are present at the same place and same time 17.3 Behavior of Waves Interference

26. Often, two or more waves are present at the same place and same time 17.3 Behavior of Waves Interference Constructive Interference

27. Often, two or more waves are present at the same place and same time 17.3 Behavior of Waves Interference Constructive Interference

28. Often, two or more waves are present at the same place and same time 17.3 Behavior of Waves Interference Constructive Interference

29. Often, two or more waves are present at the same place and same time 17.3 Behavior of Waves Interference Destructive Interference Constructive Interference

30. Often, two or more waves are present at the same place and same time 17.3 Behavior of Waves Interference Constructive Interference Destructive Interference

31. 17.3 Behavior of Waves

33. Reflection When a wave strikes an obstacle, or comes to the end of the medium it is traveling in, at least part of it is reflected Fixed end, reflection inverted Incident wave – the wave that strikes the boundary Reflected wave – the wave that is returned as a result of reflection

34. 17.3 Behavior of Waves Reflection When a wave strikes an obstacle, or comes to the end of the medium it is traveling in, at least part of it is reflected Free end, reflection not inverted

35. 17.3 Behavior of Waves

37. Standing Waves 17.3 Behavior of Waves Wave pattern that results when two waves of the same frequency, wavelength, and amplitude travel in opposite directions and interfere node – point in a standing wave that always undergoes complete destructive interference and therefore is stationary antinode – point in a standing wave, halfway between two nodes, at which the largest amplitude occurs

38. Standing Waves 17.3 Behavior of Waves antinode node

39. 17.3 Behavior of Waves

41. Waves in 2 Dimensions 17.3 Behavior of Waves

44. Refraction 17.3 Behavior of Waves Refraction – The change in direction of waves at the boundary between different media The wave travels with a different speed in each of the media The frequency remains the same, however, the wavelength changes λ = v/f

45. 17.3 Behavior of Waves

46. Diffraction – The bending of a wave as it moves around an obstacle or passes through a narrow opening