Chapter 21 Sound

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

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

• 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)

                                                                              

       

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

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

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

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

Wavelength, Frequency, and Pitch

                                                

                                                                                                                                                                                                                                                              

                                              

posterior lateral

                                                                                                                   

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

http://www.naval-technology.com/contractors/sonar/kongsberg_simrad/

                                                                                                               

                              

                                                        

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.

 

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

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

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

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

• 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

Ural Owl Ear

                                                                                                                                                                                                                                                                       

         

• The Middle Ear – Sound waves vibrate the Eardrum– Eardrum is a Thin membrane that stretches

across the ear canal– As the eardrum vibrates, it transmits

vibrations to three small bones • Hammer • Anvil • Stirrup

• The bones amplify (intensify) the vibrations

• Similar to how a lever can change a small movement at one end into a large movement at the other end

• Ruptured Eardrum

• Inner Ear – The stirrup vibrates a second membrane

called the oral window– Inner ear is filled with fluid– Vibrations are transferred to hair tipped cells

in the cochlea– Different sounds vibrate the hairs differently– Cells generate signals containing information

about the frequency, intensity, and duration of the sound

• The nerve impulse travels to the brain along the auditory nerve

How does your ear work ?

                                                    

Watch the video (Real Player needed)

                                                                 

high resolution low resolution

                                                  

Hearing Loss

• The ear can be damaged by disease, age, and exposure to loud sounds

• Constant exposure to loud sounds can damage the hair cells in the cochlea

• If hair cells die, hearing loss occurs because mammals can not produce new hair cells

• Higher frequency hearing is usually the first to be lost

• Soft consonants sounds such as s, f, h, sh, ch are hard to hear

• People with high frequency hearing loss have trouble distinguishing these sound during conversation