Waves and Sound

1. Waves and Sound

2. Basic Sound Wave Characteristics • Sound is produced when something vibrates in a medium that can carry the vibration. • In most cases the medium which with we are most familiar is AIR. • However other mediums also carry vibration waves – solids and liquids also can carry vibration • Mechanical wave • Longitudinal wave

3. Diagram of a Sound Wave • objects vibrate, causing air molecules in their vicinity to vibrate, which then radiates outward from object tuning fork with stroblight http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/waves/tfl.gif

4. Speed of Sound • Depends only on the medium the wave is traveling through • Medium can be affected by temperature, with greater temp = greater speed • More elastic mediums = greater speed (**elasticity means ability of molecules to move but also to resume their original position) • Speed of sound animation • In various mediums: • Diamond – 14,000 m/s • Steel – 5,100 m/s • Water – 1,300 m/s • Air – 340 m/s

5. Thunder vs Lightning

6. Loudness • Physiological sensation • Intensity proportional to amplitude2 • Measured decibels (dB) • Higher dBs  louder volume • Logarithmic, based on powers of 10 • 85 dB + cause hearing loss over time • 180 dB cause immediate damage • 8 hours at 90 dB causes damage

7. The chart on the left is a representation of different sounds around us and their volume in decibels.

8. The picture above is a wave file of someone singing.

9. A measure of how high or low a sound is Pitch depends on the frequency of a sound wave For example, Pitch • Low pitch • Low frequency • Longer wavelength • High pitch • High frequency • Shorter wavelength

10. Frequency – Audible Ranges • Humans • Can hear 20 Hz to 20 KHz • Best hearing within 100 – 2000 Hz • Animals • Dogs can hear up to 50 KHz • Cats can hear up to 60 KHz • Bats and whales can make and hear up to 120 KHz

11. The Doppler Effect - Wavelength Shift Due to Motion. Big Bang Doppler Effect The Doppler EffectFire Engine siren

12. Boundary Behaviors • A boundary is a place where conditions change.

13. Reflection • Bouncingback of a wave after it strikes a barrier that does not absorb the energy. • An echo is a sound wave that has beenreflected Barrier

14. The angle of the reflected wave to the normal must equal the angle of the incident wave to the normal.

15. sonar Used to locate underwater objects and distances. ***Reflection**

16. Sonograms: Ultrasonic waves (about 20,000 Hz) used to create images of fetuses in the womb Regular sonogram 3D sonogram

17. Why does the pencil appear to be broken when placed in a beaker of water??

18. Refraction:Bending of waves due to a change in speed (this occurs because the wave changesmediums)

20. Refraction

21. Diagrams Incident ray normal wavefronts slow fast fast slow refracted ray Slow to fast, bends away from normal Fast to slow, bends towards normal

22. The wave approaching a boundary is called the incident wave. • The wave moving away from a boundary is the reflected or refracted • The normal is a line perpendicular to the boundary, marked where an incident wave or ray crosses

23. Diffraction • Bendingof waves around the edge of a barrier, or through openings in a barrier

25. In sound, this is called damping – occurs even through air

26. Wave interference Def. - Interference is the result of two or more waves passing through a medium at the same time. There are two types of Wave interference: 1. Constructive Interference 2. Destructive Interference

27. Wave interference • Constructive Interference:two crests meet and make a wave with a bigger amplitude.

28. Wave interference • Destructive Interference:one crest & one trough meet and make a wave with a smaller amplitude.

29. Interference in Sound Wave Motion Interference Ripple Tank • Guy’s ear is where a compression of one sound wave meets the rarefaction of another – does he hear the sound loudly or softly? • Guy’s ear is where compression meets compression – does he hear the sound loudly or softly? Sound PhET

30. Music • One single frequency played on one instrument would not be very exciting • Music is made up of combined sound waves of different frequencies, from one or more instruments • Whole number ratios between frequencies necessary for music to sound pleasant • Causes regular and repeating resultant waves • 3rd harmonic is 320 Hz, 4th harmonic is 640 Hz, 5th harmonic is 960 Hz (a twelfth above 3rd Harmonic, E3)

31. Harmonies, Octaves, and Fifths

32. Noise • Results when there is no discernible pattern of frequencies (no whole number ratios, or regular or repeated patterns)

33. Beats • fluctuations in the intensity produced by the superposition of 2 waves at slightly different frequencies • Beat frequency is how many fluctuations in volume there areper second,measured in Hz • Tuning instruments

34. Resonance • Almost everything can vibrate, and everything has at least one natural frequency • Drop a pencil, you make it vibrate • Pluck a guitar string, it vibrates • When applied frequency (from dropping or plucking) matches natural frequency, constructive interference results in increased amplitude and a standing wave is formed – this is resonance • “Noise” comes from objects with many, irregular frequencies that produce complex sound waves with no pattern

35. Applications of Resonance • The Brown NoiseYouTube - The Brown Note Clip • Shattering a glassYouTube - breaking a wine glass using resonance • Tacoma Narrows BridgeYouTube - Tacoma Narrows Newsreel

36. 2. As the frequency of a wave increases, the period of the wave ___. a. decreases b. increases c. remains the same 3. Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing flapping is ____ sec. 4. Olive Udadi accompanies her father to the park for an afternoon of fun. While there, she hops on the swing and begins a motion characterized by a complete back-and-forth cycle every 2 seconds. The frequency of swing is _________. 5. A child in a swing makes one complete back and forth motion in 3.2 seconds. This statement provides information about the child's a. speed b. frequency c. period

37. 6. The time required for the sound waves (v = 340 m/s) to travel from the tuning fork to point A is ____ .

38. 7. An ocean wave has an amplitude of 2.5 m. Weather conditions suddenly change such that the wave has an amplitude of 5.0 m. The amount of energy transported by the wave is __________. a. halved c. quadrupled b. doubled d. remains the same 8. A teacher attaches a slinky to the wall and begins introducing pulses with different amplitudes. Which of the two pulses (A or B) below will travel from the hand to the wall in the least amount of time? Justify your answer.

39. 9. The teacher then begins introducing pulses with a different wavelength. Which of the two pulses (C or D) will travel from the hand to the wall in the least amount of time ? Justify your answer.

40. 10. The speed of a wave depends upon (i.e., is causally affected by) ... a. the properties of the medium through which the wave travels b. the wavelength of the wave. c. the frequency of the wave. d. both the wavelength and the frequency of the wave. • 11. Two waves are traveling through the same container of nitrogen gas. Wave A has a wavelength of 1.5 m. Wave B has a wavelength of 4.5 m. The speed of wave B must be ________ the speed of wave A. • One-ninth c. the same as • One-third d. three times larger than

41. 12. The number of nodes in the standing wave shown in the diagram at the right is ____. a. 6 b. 7 c. 8 d. 14 13. Of all the labeled points, destructive interference occurs at which point(s) ____.

42. Lenses refract waves to a focal point Deep water is FASTER than shallow water Cinema Classics (Side C) 61, 62