2. Physics 1

3. What is a wave? A wave is: an energy-transferring disturbance moves through a material medium or a vacuum

4. Categories of Waves Mechanical – require a material medium Medium – state of matter (solid, liquid, gas, plasma) Electromagnetic – can move through empty space (vacuum)

5. Types of Waves In a transverse wave, the displacement of the particles of the medium is perpendicular to the direction of wave motion.

6. Types of Waves Transverse Wave

7. Types of Waves In a longitudinal wave, the displacement of the particles of the medium is parallel to the direction of wave motion.

8. Types of Waves Longitudinal Transverse compression rarefaction

9. Speed of Sound – Elasticity How much a material will compress under pressure Material wants to maintain its shape (e.g. steel) rigid material LOW elasticity HIGH speed of sound (FAST) Material easily deforms (e.g. rubber) flexible material HIGH elasticity LOW speed of sound (SLOW)

10. Speed of Sound - Density Dependent on material type Fastest in solids Then liquids Then gasses Within a single phase (solid/liquid/gas) – Density has biggest impact on speed More dense, faster sound Within a single medium (e.g. air) temperature can impact speed

11. Speed of Sound

12. For the speed of sound in air, where t c is in degrees Celsius Higher temperature – faster speed of sound

13. Intensity of Sound The sound intensity is the sound power that passes perpendicular through a surface per unit of surface area.

14. Intensity of Sound If a source emits sound uniformly in all directions, one can imagine the energy spreading out in a spherical pattern.

15. Intensity of Sound The smallest sound intensity audible to the human hearing is 1 x 10 -12 W/m 2. This intensity is called the threshold of hearing (I 0 ). Since human hearing has a wide range, the intensity of audible sounds is compared to the intensity at the threshold of hearing.

16. Intensity of Sound The sound intensity of a vacuum cleaner is around 1 x 10 -5 W/m 2. Comparing this intensity to the threshold of hearing,

17. Intensity of Sound Due to the large comparison, it is more appropriate to express this relative intensity (  ) in a logarithmic scale.

18. Intensity of Sound

19. IntensityDecibels # times greater than Threshold of Hearing (TOH) Instant Perforation of Eardrum 1*10 4 W/m 2 160 dB10 16

20. Wave Characteristics frequency ( f ) period ( T ) amplitude (A) phase wavelength ( ) speed ( v )

21. Wave Characteristics The frequency (f) of a wave is the number of complete vibrations (cycles) per unit of time. 1 cycle per second = 1 hertz (Hz)

22. Wave Characteristics The period (T) of a wave is the time for the completion of a cycle. Measured in seconds.

23. Wave Characteristics The amplitude (A) of a wave is the maximum displacement of the particles in a medium from equilibrium. (“height from rest to crest”) related to the energy in the wave. Higher amplitude = more energy higher frequency shorter wavelength

24. Wave Characteristics The phase of a wave describes the position and direction of any particle in a wave-carrying medium.

25. Wave Characteristics

26. The wavelength ( ) of a wave measures the distance between any two consecutive points in- phase.

27. Wave Characteristics The speed (v) of a wave depends on the properties of the medium through which it is traveling. v = d = = f t T

28. Frequency of Sound The perceived frequency of an observer or pitch ( f o ) of an emitted frequency of a sound source ( f s ) depends on whether the observer or the source are in motion. The ACTUAL emitted frequency does NOT change!!! http://www.acs.psu.edu/drussell/Demos/doppler/doppler.html http://library.thinkquest.org/27948/doppler.html

29. Frequency of Sound Source and Observer at rest

30. Frequency of Sound f o f o =frequency perceived by observer f s f s =frequency emitted by source v o v o =velocity of observer v s v s =velocity of source v v =velocity of sound

31. Frequency of Sound v s v s =velocity of source  - (negative) when moving TOWARD observer  + (positive) when moving AWAY from observer v o v o =velocity of observer  - (negative) when moving AWAY from source  + (positive) when TOWARD source v v =velocity of sound

32. Doppler Effect – Moving Source Moving Source

33. Doppler Effect – Moving Source TOWARDS observer Wavelength gets smaller as source moves closer to observer Frequency gets faster/higher/bigger pitch gets higher

34. Doppler Effect – Moving Source AWAY FROM observer Wavelength gets longer/smaller as source moves away from observer Frequency gets smaller/lower pitch gets lower

35. Frequency of Sound v s v s =velocity of source  - (negative) when moving TOWARD observer  + (positive) when moving AWAY from observer v o v o =velocity of observer  - (negative) when moving AWAY from source  + (positive) when TOWARD source v v =velocity of sound

36. Doppler Effect – Moving Observer Moving Observer

37. Doppler Effect – Moving Observer TOWARDS source Wavelength gets smaller as observer moves closer to source Frequency gets faster/higher/bigger pitch gets higher

38. Doppler Effect – Moving Observer AWAY FROM source Wavelength gets longer (bigger) as observer moves away from to source Frequency gets slower/lower/smaller pitch gets lower

39. Sonic Booms http://www.acs.psu.edu/drussell/Demos/doppler/doppler.html http://www.falstad.com/ripple/

40. Breaking sound barrier http://video.today.msnbc.msn.com/today/4941411 9#49414119 http://video.today.msnbc.msn.com/today/4941411 9#49414119 http://www.wimp.com/breaksbarrier/

41. Electromagnetic Spectrum f f

42. Wave Properties The direction of propagation of the advancing wave is perpendicular to the wave front. This is due the wave property of rectilinear propagation.

43. Wave Properties fixed end free end

44. Wave Properties When wave encounters a boundary between two media of different propagation speed, some wave energy can be turned back. This is called the wave reflection.

45. Wave Properties incident wave reflected wave

46. Refraction - the bending of a wave caused by a change in speed as the wave moves from one medium to another.

47. Wave Properties When a wave passes through an opening in a barrier, the wave energy will spread out beyond the barrier. This is called the wave diffraction.

49. Wave Properties Principle of Superposition - When two waves traveling independently through the same medium, the resultant displacement of any particle at a given time is the vector sum of the displacements that the individual waves acting alone would give it.

50. Wave Properties When two wave pulses encounter each other in a medium, the wave pulses will superpose beyond the barrier. This is called the wave interference.

51. Wave Properties Constructive Interference

52. Wave Properties Destructive Interference

53. Standing Waves A standing wave is the result of two waves of the same frequency and amplitude traveling in the opposite directions through the same medium.

54. Standing Waves A point of no disturbance in a standing wave is called a node. A point in standing wave where the amplitude is maximum is called an antinode.

55. Standing Waves The fundamental frequency (or natural frequency) of a medium occurs when it vibrates with the simplest standing wave – 2 nodes + 1 antinode.

56. Standing Waves The harmonic of a wave is a component frequency of the wave that is an integer multiple of the fundamental frequency. 1 st Harmonic = 5 2 nd Harmonic = 10 3 rd Harmonic = 15 4 th Harmonic = 20

57. Harmonic Series

58. Beats Beats are the periodic and repeating fluctuations heard in the intensity of a sound when two sound waves of very similar frequencies interfere with one another. Beat Frequency … Beat frequency is absolute value of difference between two close frequencies

59. Resonance The frequency or frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed or somehow disturbed is known as the natural frequency of the object. The tendency of one object to force another adjoining or interconnected object into vibrational motion is referred to as a forced vibration.

60. Resonance Resonance occurs when two interconnected objects share the same vibrational frequency. When one of the objects is vibrating, it forces the second object into vibrational motion. The result is a large vibration.

61. Resonance Tacoma Narrows Bridge http://www.youtube.com/watch?v=3mclp9QmCGs