Exploring Sound Waves: From Creation to Perception

1. Chapter 21 Sound

2. What is Sound • All sounds are produced by something that vibrates • A wave carries energy from one place to another and without transferring matter • The vibrating object causes air molecules to move back and forth • As these air molecules collide with those nearby , they cause other molecules to move back and forth • A sound wave is a compressional wave, like a wave moving through a coiled spring • In sound waves, air molecules move back and forth along the direction of the wave

7. Making Sound Waves • When an object vibrates, it exerts a force on the surrounding air • For example, as the end of the tuning fork moves outward into the air, it pushes the air molecules together • As a result, a region where the air molecules are closer together, or more dense, is created • This region of high density is called a compression • When the tuning fork moves back it causes an area of low density called rarefaction • The compression and rarefaction move away from the tuning fork as molecules collide with one another

8. Sound waves can be described by its wavelengths and frequency • Wavelength is the distance between two consecutive compressions or two consecutive rarefaction • Frequency of a sound is the number of compressions or rarefactions that pass by a given point in one second • The unit of frequency is the number of wavelengths per second, or Hertz (Hz)

14. Speed of Sound • Speed of sound varies because of temperature and material it is passing through • Sound moves faster in solid then liquids or gases because the particles that makes solid up are closer together • Sound is slowest in gases because molecules are farther apart • As the temperature heats up its molecules move faster, so they collide more frequently • More frequent the collision the faster sound travels • 0* C sound travels a 331m/s, 20*C 343m/s

17. Amplitude and Loudness • Loudness is the human perception of how much energy a sound wave is carrying • The amount of energy a wave carries depends on its amplitude • Higher amplitude- more compressed the particles in a compression are and the farther they are spread out in a rarefaction • Higher amplitude means more energy and louder

20. Decibel Scale • Scale used to describe sound waves • Increase in 10 decibels means that the energy carried by the wave has increased 10 times • Increase in 20 decibels, energy increases 100 times • Increase in 30 decibels, energy incresed 1000x • Hearing Damage begins to occur at 85 dB • Jet Plane = 150 dB • Whisper =15dB • Lawn Mower =110

23. Frequency and Pitch • Pitch of a sound is how high or low it sounds • Pitch corresponds with frequency of the sound • High the pitch the higher the frequency • Lower the pitch the lower the frequency • Human ear can detect sound waves with frequencies between about 20Hz and 20,000Hz. • Dogs can hear frequencies up to almost 50,000 Hz • Dolphins and Bats can hear frequencies as high as 150,000 Hz. • Higher pitch - shorter wavelengths, Lower pitch – Longer Wavelength • Length and thickness of your vocal cords help determine your pitch • Short thinner vocal cords vibrate at higher frequencies, results in higher voices • Muscles in throat can stretch the vocal cords tighter, letting people vary their pitch

24. Wavelength, Frequency, and Pitch

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27. Echoes • A echoes is a reflected sound wave • Sound waves reflect off of hard surfaces • Sonar systems use sound waves to map out objects underwater • The amount of time it takes for echoes to return depends on how far away the reflecting surface is • Echolocation – the ability to emit high pitched squeaks and listen for echoes. Used to navigate and hunt • Bats and dolphins use echolocation

34. Dolphins produce high frequency clicks that pass through the melon. These sound waves bounce off objects in the water and return to the dolphin in the form of an echo.

35. Doppler Effect • The change in a frequency that occurs when the source of the sound is moving relative to a listener is the Doppler effect • Occurs whether the sound source or the listener is moving • As you move closer to the source you encounter each sound wave a little earlier • The closer you get the higher the pitch • When you move away , each sound wave takes longer to reach you, you hear fewer wavelength, which results in a lower pitch • Radar guns used to determine speed of cars and baseballs use the Doppler Effect

39. Diffraction • Diffraction means that sound waves can bend around obstacles or spread out after passing through a narrow opening • The amount of diffraction depends on the wavelength • If Wavelength is much smaller than the obstacle, almost diffraction occurs • If wavelength is closer or larger then the size of the obstacle, the amount of diffraction increases

42. Using Sound Waves • Ultrasound – using high frequency sound waves as an alternative to some surgeries • Kidney stones and gall stone sometimes can be broken up using ultrasound • Used to exam a developing fetus, and internal organs

45. The Ear • The ear is a complex organ that is able to detect a wide range of sounds • Has three parts • Outer Ear • Middle Ear • Inner Ear

47. The Outer Ear • Collects sound waves and directs them into the ear canal • Shaped like a funnel to collect sound waves • Animals that rely on hearing to locate predators or pry often have large ears and can be adjusted • Rabbits and Owls