2. Waves and Sound

3. Waves - “rhythmic disturbances” which carry energy disturbances- any interruption of the normal course of events In case you were wondering… rhythm- a regularly repeating pattern

4. - can travel through matter or empty space medium - the type of matter that a wave travels through - can be a solid, liquid, or gas - waves that need a medium are called mechanical waves - waves that do not need a medium are called electromagnetic waves

5. The two main types of mechanical waves are transverse and longitudinal (or compressional) waves

6. Parts of a Transverse Wave Crest-the highest point of the wave Trough- Rest Position- the lowest point of the wave the position of the medium when energy is not passing through it

7. Amplitude- Wavelength- the distance from the rest position to either the crest or the trough the distance from one point on a wave to the exact same point on the next wave - the Greek letter lambda ( ) is used as the symbol for a wavelength

8. crest trough rest position amplitude

9. Other parts of a wave you should know… Frequency-the number of crests that pass a given point each second - based on the size of the wavelength - can be changed all of the frequencies of energy can be shown on the electromagnetic spectrum (which will be discussed in a later chapter) - measured in Hertz (Hz)

10. Velocity - how fast the waves are traveling when they pass that point - can be calculated using the formula velocity = the size of the wavelength x the frequency or… v = x f

11. also… the speed of a wave in a particular medium is constant therefore.. if you want to change the frequency, you must change the wavelength:

12. If you want toYou must increase the frequencydecrease the wavelength decrease the frequencyincrease the wavelength

13. modulation- to change to change the number of waves that pass a point each second frequency modulation (FM)- amplitude modulation (AM)- to change the size of the waves that are passing a given point this is what you are doing when you are tuning your AM/FM radio!!!

14. Parts of a Longitudinal (Compressional) Wave Like a transverse wave, longitudinal waves have crests, troughs, and wavelengths. They also have two other parts that transverse waves do not:

15. Compressions- areas where the waves are packed tightly together areas where the waves are spread far apart Rarefactions-

16. CompressionsRarefactions Wavelength (includes one set of compressions and one set of rarefactions)

17. So what is the difference between a transverse and longitudinal wave? the biggest difference is how the wave moves compared to how the medium moves: Besides the way they look,

18. In a transverse wave, the medium moves at a 90  angle to the direction of the wave- medium wave

19. In a longitudinal wave, however, the medium and the wave move in the same direction medium wave

20. Moving through Media Plural of the word “medium” The speed at which a wave travels depends upon two things: 1.) the type of medium through which the wave is traveling waves travel fastest through solids, then liquids, then gases (like air)

21. 2.) the temperature of the medium - as the temperature of the medium increases, so will the speed of the wave COOLERWARMER SOLID LIQUID GASSOLID LIQUID GAS Fastest- a warm solid Slowest- a cold gas

22. Some other terms you ought to know… Pitch-the “highness” or “lowness” of a sound - depends on the frequency of the waves:   Higher FrequencyHigher Pitch Lower FrequencyLower Pitch

23. Humans can hear frequencies between 20Hz and 20,000Hz - frequencies below 20Hz are called subsonic - frequencies above 20,000Hz are called ultrasonicor supersonic

24. Intensity - the amount of energy in each wave - depends on the amplitude: Higher Amplitude   Lower AmplitudeLess Intensity More Intensity -the “human perception” of sound intensity Loudness - varies from person to person

25. Intensity and loudness are both measured in decibels (dB) some examples… Type of SoundLoudness in Decibels rustling of leaves normal talking vacuum cleaner lower limit of pain rock concert space shuttle take-off 15 dB 65 dB 85 dB 120 dB 200 dB 115 – 160 dB

26. Doppler Effect - the increase or decrease in the frequency of sound waves due to the motion of an object - caused by waves getting pushed together or stretched apart - makes objects coming towards you sound like they have a higher pitch and objects moving away from you sound like they have a lower pitch

27. Normal WavesDoppler Effect For example-

28. Doppler Effect #1Doppler Effect #2

29. Interactions of Waves

30. there are four types- 1.) Reflection - when a wave strikes an object and bounces off - occurs in all types of waves - the angle at which the light bounces off can be determined by using the

31. Law of Reflection Remember, a law explains what will happen, but not why, and it can be proven states that “The angle of incidence is equal to the angle of reflection” Okay, but what is the “angle of incidence” and an “angle of reflection”?

32. Angle of Incidence- the angle at which waves strike an object Angle of Reflection- the angle at which waves are reflected off a surface for example-

33. Angle of Incidence Angle of Reflection equals

34. 2.) Refraction - the bending of waves - caused by the change of speed that occurs when a wave moves from one medium to another - the greater the change in speed, the more the light gets bent

35. refraction

36. Refraction also depends on the size of the wavelength: violet waves (which have small wavelengths) get bent the most red waves (which have longer wavelengths) get bent the least

37. when light hits water droplets in the atmosphere, the light gets refracted. this results in RAINBOWSRAINBOWS

38. 3.) Diffraction - the bending of waves around a barrier - most (but not all) waves can be diffracted - longer wavelengths are easier to diffract than shorter wavelengths

39. 4.) Interference - the combining of two or more waves - there are two types: a. if the crests or compressions of one set of waves combine with the crests or compressions of another set of waves, the result is a wave that is This is called Constructive Interference and MORE INTENSE.BIGGER

42. b. if the crests or compressions of one set of waves combine with the troughs or rarefactions of another set of waves, they will This is called Destructive Interference cancel each other out

45. Music & Noise

46. Music (frequencies which compliment the melody) and harmonies (a specific pattern of sound frequencies), a melodya rhythm,- usually includes - specific pitches and sound qualities following a regular pattern

47. both music and noise are caused by a combination of sound waves of different frequencies: Noise - sounds with no specific pitch or pattern

48. Noise- Music-

49. white noise - for some reason, white noise has a very relaxing effect on humans - the result when all frequencies of sounds are present in equal amounts

50. Natural Frequencies - if these waves are between 20Hz and 20,000Hz, we call these frequencies “sound” - These waves are called natural frequencies - because all objects vibrate, all objects create waves. “sound waves”

51. - if these waves come in contact with another object that has the exact same natural frequency, the object will begin to vibrate more forcefully. This is called resonance examples…

52. - most objects vibrate at more than one frequency - this unique pattern is called the sound quality - in addition, the combination of frequencies at which an object vibrates is unique to that object, much like a fingerprint

53. Also, causing overtones if the vibrating object is large enough, small parts of the object will begin to vibrate on their own, for example…

54. overtones

55. Making Music - notes can be put together in a specific pattern called a scale - sounds with specific frequencies are called notes

56. - a scale usually has eight notes - scales can start on any letter - when reading music, these notes are represented by the letters “A” through “G” ( a scale with more is called a “chromatic” scale)

57. - if the pitch is varied only a little, you can (higher frequency)or sharp (lower frequency)make the notes flat

58. - the difference in frequency between the 1 st note and the 8 th in a scale is called an octave (note: the first and last notes on a scale are always the same letter) 1 octave

59. one last term… the study of soundAcoustics-