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SOUND travels in Longitudinal Waves

• Particles vibrate back and forth along path wave travels

• Compression = particles are crowded

• Rarefaction = particles less crowded

science-class.net/Notes/Notes_waves.htm

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Properties of Sound• Speed varies based on:

– Medium, temperature, density, elasticity

• Pitch: sensation of frequency(HERTZ)– Low pitch = low frequency– High pitch = high frequency

• Intensity: amount of energy in a wave; greater amplitude = more energy = louder sound

• Loudness is measured in DECIBELS

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Decibel Scale Measures IntensitySource Intensity Level

Threshold of Hearing (TOH) 0 dB

Rustling Leaves 10 dB

Whisper 20 dB

Normal Conversation 60 dB

Busy Street Traffic 70 dB

Vacuum Cleaner 80 dB

Threshold of Damage 100 dB

iPod at Maximum Level 100 dB

Front Rows of Rock Concert 110 dB

Threshold of Pain 130 dB

Military Jet Takeoff 140 dB

Instant Perforation of Eardrum 160 dB

http://www.glenbrook.k12.il.us/gbssci/Phys/Class/sound/u11l2b.html

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Pitch

• How high or low a sound is

• Depends on how fast the particles vibrate

• Low – trombone, bass, tuba

• High – piccolo, violin, viola, flute, xylophone

• Soprano – 1000 Hz

• Thunder – 50 Hz

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Speed of Sound at 20ºC

• Air = 342 m/s (764 miles/hour) at 20°C

• Seawater = 1530 m/s

• Steel = 5200 m/s

• Speed Changes w/ Temp

• Speed = 342 m/s + .6ΔT (for air only)

• MACH 1 = 342 m/s : MACH 2 = 684 m/s

• Light travels through air at a speed of approximately 300,000,000 m/s

• Almost 900,000 times the speed of sound

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Distance to a source

• Distance = Speed of Sound x Time(sec.)

• Measure time from lightening and thunder

• Distance = 342m/s X 5 sec» = 1710 meters (1.06 miles)

• Be sure to correct speed

related to temperature

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Doppler Effect

• Causes pitch to rise as approaching and drop as going away

http://www.colorado.edu/physics/2000/applets/doppler2.html

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Echo

• Reflection of a sound wave• Time delay between the production of a

sound and the arrival of a reflection of that sound off a distant barrier

• Distance to barrier calculations: If Echo is heard in 3 seconds(20º)

• distance = velocity • (time/2) = 342 m/s • (3s ÷ 2) = 513 m

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Acoustics

• Sound waves from various sources interact in an auditorium.

• We attempt to control the sounds by absorbing waves at the perimeter (walls)

• designing the angles of the wall

• putting softer material on the walls to absorb extra sound.

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Interference• Two waves can

occupy the same space

• The overlapping of two + more waves

• Constructive Interference increases amplitude

• Destructive Interference decreases amplitude

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Human Vocal Chords

• When air passes, they vibrate causing sound that we learn to control causing speech.

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Six steps to Speech

• Breath - controlled by muscle (diaphragm) contracting and forcing air out of lungs

• Vocal Chords vibrate because of the air

• Bucal Cavity(back of throat) – shaped for sounds

• Tongue – adjusted for sounds

• Teeth – placed for sounds

• Lips – adjusted for sounds

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Human Ear

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Steps of Hearing• Ear Flap helps direct waves into ear canal• Ear Drum vibrates when struck by waves• 3 Bones (hammer, anvil & stirrup) intensify

vibration through Middle to Inner Ear• Cochlea liquid is moved causing hairs to

move with frequency of vibration• Nerves attached to hairs carry impulse to

the portion of the Brain used to interpret the “electrical impulses” into Sound

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Music vs. Noise• Music produces a sound wave with a

repeating patterns of frequency and amplitude.

• Noise can be described as any undesired sound that includes a random mix of pitches and amplitudes

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Source of sound in instruments• Strings – vibration caused by plucking or

bowing. Pitch controlled by length, tightness and diameter of string

• Brass -- vibration caused by lip vibration against a mouthpiece. Pitch controlled by adjusting breath, lips and length of column

• Woodwinds – Breath vibrates a reed. Pitch is controlled by length of air column.

• Percussion – Vibrations caused by concussion. Pitch controlled by material, size and part vibrated.

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Overtones• Fundamental tone: Chosen standard tone

wavelength• First Overtone: Wavelength that is ½ standard• Second Overtone: Wavelength that is 1/3

standard• Third Overtone: Wavelength that is ¼ standard• One more wave than name.

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Sonar• Reflecting sound waves in water off of

boats, submarines, or sunken objects and the sea floor and interpreting the reflection

• Distance, direction and speed of objects can be calculated.

• Based on time of travel of the sound wave in the water at the ambient temperature.

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Ultrasound• Frequencies above 20,000 hertz• Dog whistles-too high for us to hear but bothers dog/cats• Echolocation—Bats and Dolphins—producing a sound which

then echoes off an object or surface and then detected by the animal

• Ultrasonic cleaners—jewelry • Medicine

– Sonogram is a picture made of the inside of the body by interpreting bounced sound

– Using focused sound to destroy unwanted tissue inside the body– Kidney stones

– Toothbrushes--Sonicare• Camera range finders — infrared or ultrasonic

–

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Infra-sound

• Very low pitched sound –less than 20 Hz

• Communication/Location can occur over 100’s of miles if in water– Elephants – 10-20 miles in air– Whales – 100’s of miles in water– Humans have reported detecting this sound as a

rumbling in your gut that you feel

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Hearing Ranges of Animals

• Humans range from 20 Hz to 20,000 Hz • Dogs range from 50 Hz to 45,000 Hz• Cats range from 45 Hz to 85,000 Hz• Bats rely on sound echolocation for navigation

and hunting and can detect ultrasonic frequencies as high as 120,000 Hz.

• Dolphins can detect ultrasonic frequencies as high as 200,000 Hz

• Elephants can detect infrasound, having an audible range from approximately 5 Hz to approximately 10,000 Hz

http://www.glenbrook.k12.il.us/gbssci/Phys/Class/sound/u11l2a.html

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Sound Math

• 1. What is the speed of sound when the air is 36º Celcius? Answer in m/sec. (351.6)

• 2. What is the speed of sound when the air is -10º Celcius? Answer in m/sec. (324)

• 3. What is the speed of a jet(m/sec) going Mach 2.35 when the air is 20º C?(803.7)

• 4. How far away is the lightning bolt when there is a 6 second wait for the thunder? The temperature is 25º C. (2070)

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• 5. How far away is the canyon wall if the echo is heard 5 sec. later? (15ºC) (847.5)

• 6. How far away is a submarine detected by sonar if the ping is heard 4 seconds after release at 20ºC? (3060)

• 7. How far could a sound vibration travel through a steel rail in .75 sec. at 20º C? (3900)

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Math Solutions• 1. What is the speed of sound when the air

is 36º Celcius? Answer in m/sec.

S=342 + .6(16) = 351.6 m/sec

• 2. What is the speed of sound when the air is -10º Celcius? Answer in m/sec.

S=342 + .6(-30) = 324 m/sec

• 3. What is the speed of a jet (m/sec) going Mach 2.35 when the air is 20º C?

S = 342 * 2.35 = 803.7 m/sec

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• 4. How far away is the lightning bolt when there is a 6 second wait for the thunder? The temperature is 25º C.

S = 342 + .6(5) = 345 m/sec

Distance = Speed * Time

D = 345 m/sec * 6 sec = 2070 meters

• 5. How far away is the canyon wall if the echo is heard 5 sec. later? (15ºC)

S = 342 + .6(-5) = 339 m/sec

D = 339 m/sec * 5/2 = 847.5 m

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• 6. How far away is a submarine detected by sonar if the ping is heard 4 seconds after release at 20ºC?

Distance = 1530m/sec * 4sec/2

= 3060 meters

• 7. How far could a sound vibration travel through a steel rail in .75 sec. at 20º C?

Distance = 5200m/sec * .75 sec

= 3900 m

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• 1. What is the speed of sound when the air is 36º Celcius? Answer in m/sec.• S=342 + .6(16) = 351.6 m/sec • 2. What is the speed of sound when the air is -10º Celcius? Answer in m/sec.• S=342 + .6(-30) = 324 m/sec • 3. What is the speed of a jet (m/sec) going Mach 2.35 when the air is 0º C?• S = 342 * 2.35 = 803.7 m/sec • 4. How far away is the lightning bolt when there is a 6 second wait for the

thunder? The temperature is 25º C.• S = 342 + .6(5) = 345 m/sec• Distance = Speed * Time• D = 345 m/sec * 6 sec = 2070 meters• 5. How far away is the canyon wall if the echo is heard 5 sec. later? (15ºC)• S = 342 + .6(-5) = 339 m/sec• D = 339 m/sec * 5/2 = 847.5 m • 6. How far away is a submarine detected by sonar if the ping is heard 4 seconds

after release at 20ºC? • Distance = 1530m/sec * 4sec/2• = 3060 meters• 7. How far could a sound vibration travel through a steel rail in .75 sec. at 20º

C? Distance = 5200m/sec * .75 sec• = 3900 m