Chapter 16

Sound Waves

I. Sound is a wave.A. Sound is a type of mechanical wave.

1. produced by a vibrating object and travels through matter

2. disturbances are vibrations-rapid back and forth motions

3. medium vibrates in the same direction as the wave travels and transfer energy

4. How Sound Waves Are Produceda. started by vibrations that send out waves in

all directionsExample: vocal cords- relax when you

breathe to allow air to pass through the windpipe; they tense up when you are about to sing or speak

5. How Sound Waves Are Detected a. Shape of the ear (like a satellite dish) helps collect sound waves b. Reflected into the ear canal (tiny tube) c. Waves strike the eardrum ( thin skin-like membrane at the end of the ear canal) and

they vibrate. d. Vibrations transfer from the eardrum through

the tiny bones in the middle ear (hammer, anvil and stirrup.)

e. Vibrations reach the cochlea (30,000 hair cells) and vibrate (bend) the tiny hairs causing the

cells to send impulses along the nerves to the brain.

f. When your brain processes these signals, you HEAR A SOUND!

B. Sound waves vibrate particles.1. You cannot see the motion of waves in air.2. Imagine striking a drum: a. Drum skin vibrates very rapidly (pushing in

and out) and pushes against particles in the air. Particles become bunched together (compressions).

b. When the skin is pushed in the opposite direction, it leaves an open space for the particles to rush back in and fill it.

c. A listener hears all of these vibrations. P. 520

***A vacuum is empty space and has no particles so sound cannot travel through it!

C. The speed of sound depends on its medium.1. Sound travels more slowly than light and at

different speeds.2. Two factors affect the speed of sound: type of medium and the temperature

3. The Effect of the Material a. Sound waves travel faster through liquids than in

air because liquids are denser (closely packed) ***Divers would hear a sound quicker underwater

than people above water. b. Sound waves travel through elastic solids as well.

2. The Effect of Temperature a. Sound travels faster through higher temperatures (hot air). Example: Yelling outside on a hot day very a cold winter morning

16.116.1

II. Frequency determines pitch.A. Pitch depends on the frequency of a sound

wave. 1. Pitch- high or low of sounds 2. high frequency=short wavelengths= fast vibrations= high pitch (and vice versa) 3. High and Low Frequencies a. Once complete wave is a cycle b. Unit of measurement for frequency and pitch is HERTZ c. Human hearing range is 20-20,000Hz d. Infrasound- ranges below 20 hertz

Example: elephants e. Ultrasound- ranges above 20,000hertz

Example: dogs, bats, chimpanzees and dolphins

4. Natural Frequencies a. The frequency at which an object vibrates b. Constructive interference- when two different sound waves of the same natural frequency encounter one another; amplitudes add and the sound is stronger (resonance) 5. Sound Quality

a. Each musical instrument and human voice has its own particular sound- sound quality.

b. Timbre (sound quality) is explained because it’s a combination of waves. You hear the

fundamental tone.c. Overtones- higher frequency pitchesd. Affected by starts and stops- human voice

starts gently (p. 529 Oscilloscope)

B. The motion of the source of a sound affects its pitch.*** motion of the source of a sound affects the pitchExample: the pitch drops when an ambulance passes by you coming from behind.1. The Doppler Effect *** The change in perceived pitch that occurs when the source of receiver of a sound is movingExperiment: p. 530

2. Frequency and Pitch a. Sound waves that hit your ears are closer together

so the pitch and frequency is higher b. As the sound moves farther away, sound waves still come to you but they are farther apart and lower in pitch.

III. Intensity determines loudness.A. Intensity depends on the amplitude of a sound wave.

1. the more energy a wave carries, the more intense and the louder

2. measured in decibels3. greater the amplitude, more intensity and the

louder it will beB. The intensity of sound can be controlled.

1. Sound waves get weaker and weaker until sound in undetected. (amplitude decrease but

frequency and pitch stay the same)2. sound intensity is changed by adding or removing

energy (changing amplitude)Example: mufflers on cars (makes it sound lower)

3. Amplification a. Make it bigger b. Increases the strength of the electrical signal Example: adjusting stereo volume

4. Acoustics a. Scientific study of sound b. How sound is produced and received c. How sound waves behave inside a space Example: using acoustical tiles of different

shapes to absorb or redirect some of the energy of sound waves

C. Intense sound can damage hearing 1. The sensitivity of hair cells of the cochlea make hearing

possible and makes it easy to damage cells as well. 2. Noises above 130dB are especially dangerous; 140dB

are even painful.Example: Some loud factories are required to provide ear plugs for ear protection to employees.

IV. Sound has many uses.

A. Ultrasound waves are used to detect objects.

1. Echolocationa. Sending out ultrasound waves and interpreting the returning sound echoesb. Helps animals find their prey or objects in front of them

Example: bats and dolphins p. 539

Echolocation Bat Music Video

2. Sonara. Instruments that use sound waves (echolocation)

to locate objectsb. Sound navigation and rangingc. Send out ultrasound waves and use the echoes to produce an image on the screenExamples: locating submarines during war, fishing boats, to map the sea floor, find ancient sunken ships

3. Medical Uses of Ultrasound*** Not heard by humans and used at high intensities

Examples: break up kidney stones, see used to clean medical equipment, to see inside internal organs, detect the movement of fluids (blood flow) through the body, checking the health of a fetus during pregnancy

B. Sound waves can produce music.a. Clear pitches or rhythmsb. Vibrate at their natural frequenciesc. Some have different parts that vibrate to make different pitchesd. Stringed, wind and percussion- 3 main types (electronic- 4th type)

Examples: p. 541

C. Sound can be recorded and reproduced.1. The Telephone a. Long distance voice communication b. Translates and the then reproduces sounds

See p. 5422. Recorded Sound

a. Occurs in real time b. sound waves turned in to electrical signalsSee p. 543