The document discusses key properties and characteristics of sound. It defines sound as a vibration that travels through air or other mediums and can be heard. Sound waves are longitudinal waves that require a medium. The amplitude of a wave determines its volume or loudness, while frequency determines its pitch or how high or low it is. Higher frequencies have smaller wavelengths. The human ear can detect sounds between 20 Hz and 20 kHz. The speed of sound depends on the medium and temperature. Ultrasound uses high frequency sound to image inside the body. The Doppler effect causes changes in perceived frequency for moving sources due to wave compression.
2. • Incredible Human Machine video
– how sounds are perceived & produced (5:35)
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3. What is Sound?
• A sound is any vibration (wave)
traveling through the air or other
medium which can be heard when
it reaches a person's ear.
• Sounds waves are:
• Longitudinal - oscillations parallel to propagation
• Mechanical - require a medium to travel through
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4. How Sound is Created
• When an object vibrates, it creates sound
– loud, deep and long, short and high-pitched
– pure, gravely, distorted, sweet, soft, piercing, buzz
• Any sound your ear can hear is created by the
mechanical back-and-forth motion of an object
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6. Amplitude & Volume
• The amplitude of a wave determines a sound's volume.
– Volume tells how loud or soft a sound is
• determined by how much energy a wave carries.
– Amplitude describes how much energy a wave is carrying:
• more energy = greater amplitude = louder sound
• greater amplitude = taller wave or more intense compressions
Higher Amplitude Loud
Lower Amplitude
Quiet
Higher Amplitude
Lower Amplitude Loud
Quiet
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7. Decibels & Sound Volume
• Audible sound energy is
measured in decibels (dB)
– Only measures within the limits
of human hearing
• 0 is just barely audible
• 120+ causes pain/damage
– figured by powers of 10
• 20 dB is 10 x 10 times > 0dB
(100 times great than 0 dB)
• 30 dB is 10 x 10 x 10 greater
(1,000 times > 0 dB)
• Hearing damage depends on:
– sound amplitude (loudness)
– frequency (pitch) of the sound
– duration of exposure to the
sound
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8. Frequency & Pitch
• Pitch tells how high or low a sound is
– a higher pitch will have greater frequency
(more waves crammed into each second of time)
• higher frequencies have smaller wavelengths
Sample tones
Ruben's Tube video
Sand Vibration Patterns
• Nodes = areas of zero
displacement
– sand is not moved
– flame is not shot out
of holes
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9. Wavelength & Pitch
• Two things affect frequency:
Student Demo
– wavelength and wave speed
• slow moving wave pattern and small wavelength
• quickly moving wave pattern and large wavelength
• Sound waves will move at a constant speed unless:
– they are moving through different mediums
– they are moving in mediums of different temperatures
– the source creating the sound
is moving (train, ambulance, etc.)
It is usually a change in
wavelength that results in a
different pitch.
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10. More about Frequency
• Sound waves can be
absorbed by objects.
– Higher frequencies (smaller
wavelengths) are absorbed
more than lower frequencies
(bigger wavelengths).
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11. How Sound is Heard
• Sound waves are funneled by the pinna into the ear canal.
• The tympanic membrane is then vibrated like a drum by
the compressional sound waves.
• Tiny bones
(ossicles)
transfer the
wave motion
to a soft,
fluid-filled
organ in the
inner ear.
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12. The Inner Ear
• The spiral-shaped cochlea has tiny, hair-shaped cells
inside that transfer the mechanical energy (back-and-forth
motion) of the wave into electrical energy (nerve impulses).
• Your brain interprets different tone
pitches depending on which cells in
the cochlea are moved by the sound
wave passing through the fluid.
– high frequencies stimulate the base
– lower pitches make the hairs of the
apex (center) vibrate
hair cells
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13. Ears and Balance
• As your body moves, hair cells in the semicircular canals
are bent over when the fluid inside flows past them.
• Three canals oriented in 3 directional planes:
– yaw (rotation), pitch (forward/back), and roll (side to side)
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Not affected by sound waves.
14. Limits of Human Hearing
Frequencies ABOVE what humans can hear are ultrasonic waves (20,000+ Hz).
Frequencies BELOW what humans can hear are infrasonic waves (0 to 20 Hz).
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15. Speed of Sound
Medium Speed (m/s)
Gases
• Density and temperature
Air (20°C) 343 affect how fast sound will
Air (0°C) 331 travel through a medium
Liquids at 25°C – Sound travels fastest in solids,
Sea water 1533 then liquids and more slowly
Water 1493 in gases
Mercury 1450 – Sound travels faster in warmer
Methyl alcohol 1143 air than cold air
Solids
Rubber 1600
Gold 3240
Iron 5130
Pyrex glass 5640
Diamond 12000
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16. Calculating Distance with Sound
• Light travels at almost 300,000,000 meters per second
• Speed only moves at roughly 340 m/s
– This is why you always SEE lightning before you HEAR it!
• What is the formula for speed? Speed = distance/time (s=d/t)
• To figure the distance of
a storm: speed x time
– There are 1,609 meters in a
mile. (~340 x 5)
– So for every 5 seconds we
count, the storm is 1 mile
away.
Thunderstorm Calculator
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17. Ultrasound
• Ultrasound is a wave frequency higher
than is detectable by the human ear.
• A probe transmits millions of sound
pulses into the body each second.
• Some waves are reflected as they travel
through boundaries between tissues (i.e.
fluid & soft tissue, soft tissue & bone).
• Reflected waves are picked up by the
probe and relayed to the machine.
• A computer
calculates the
distance from the
probe to each
tissue boundary
using the speed of sound and the time
of each echo's return. (speed = d/t)
• The distance and intensity of each echo
is then displayed as a screen image.
• Used to "see" inside and diagnose many different body areas.
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18. Other Uses of Ultrasound
• Veterinary Medicine
• Cleaning & Disinfection
• Humidifiers
• Welding
• Pest Control
• Animal Navigation
& Communication
• SONAR
• Sonic Weapons Powerpoint Templates
19. The Doppler Effect
• As a motorcycle speeds forward, the frequency (pitch) of
the sound waves in front of the motorcycle become higher,
and the frequency (pitch) of the sound waves behind it
become lower.
• As the object making
the sound moves, the
waves get bunched up.
• "Bunched up" waves
have a smaller wave-
length, thus a higher
frequency (pitch). wavelength
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20. Moving Sound Source
A stationary sound source. Sound waves are
produced at a constant frequency, and the
wavefronts move symmetrically away from the
source at a constant speed. All observers will hear
the same frequency, which will be equal to the actual
frequency of the source.
The same source is creating sound waves at the
same frequency. However, the source is moving to
the right, so the center of each new wavefront is
slightly displaced. As a result, the wavefronts begin to
bunch up on the right side (in front of) and spread
further apart on the left side (behind) of the source.
An observer in front of the source will hear a higher
frequency, and an observer behind the source will
hear a lower frequency (pitch).
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21. Doppler Radar
How it works:
• Radar gun sends out waves
• Waves bounce off moving
objects and return to radar gun
• If the object is moving when the
wave is reflected, the frequency
of the wave will be changed - the
Doppler effect
• The gun's sensor records
the change in frequency
and uses that to calculate
the object's speed.
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22. Sonic Booms
• Science is Fun video
• When an object moves FASTER than
the speed of sound, it punches
through all the bunched up waves in
front of it, creating an audible sound
– a sonic boom is made the instant all
the bunched wave fronts join to make
one very loud (high amplitude)
longitudinal sound wave
• Mach 1 = the speed of sound
– named after Austrian physicist and
philosopher Ernst Mach
• Faster-than-sound velocities are called
supersonic speeds
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Notas do Editor
Whenever an object in air vibrates, it causes longitudinal or compression waves in the air. These waves move away from the object as sound. There are many forms of the vibration, some not so obvious. The back and forth movement of a loudspeaker cone, guitar string or drum head result in compression waves of sound. When you speak, your vocal cords also vibrate, creating sound. Blowing across a bottle top can also create sound. In this case, the air inside the bottle goes in a circular motion, resulting in sound waves being formed. Wind blowing through trees can also create sound this indirect way. Sound can also be created by vibrating an object in a liquid such as water or in a solid such as iron. A train rolling on a steel railroad track will create a sound wave that travels through the tracks. They will then vibrate, creating sound in air that you can hear, while the train may be a great distance away.
Demo: have one student stand and count out loud how many "wave" pass by. Have 3 students stand close together in a line and pass by the "counter" very slowly to generate a frequency of 3Hz. Have another group of 3 students stand arms-length apart and pass by the "counter" quickly to also generate a frequency of 3Hz. Explain that both of these waves would generate the same pitch because they have the same frequency. However, the two waves would have to be traveling in different mediums in order for this to happen.
The outer ear consists of the pinna, which is the external skin and cartilage on both sides of our heads that we think of when we hear the word “ear,” as well as the external auditory canal. The shape of the pinna is ideal to collect the sound waves, direct them down the ear canal, and vibrate the tympanic membrane, or eardrum. The eardrum separates the outer ear from the middle ear. In the middle ear, the eardrum’s vibrations move the Malleus (hammer), the Incus (anvil) and the Stapes (stirrup) bones of the middle ear, collectively known as the ossicles. With motion of the ossicles, the sound waves that first entered the ear canal have been converted to mechanical energy, and this energy is conducted toward the inner ear. Movement of the ossicles causes vibrations in the fluid of the cochlea, the hearing portion of the inner ear. As the cochlear fluid vibrates, it moves thousands of tiny hair-like nerve cells that line the cochlear walls, which serves to convert the mechanical energy of the ossicles into the requisite electrical nerve impulses. These impulses travel from the cochlea up the auditory nerve, where they are received and given meaning and relevance by the brain. The cone-shaped bone that forms the part of the skull immediately below and behind each ear is called the mastoid process. The internal ear structures and hearing processes are protected deep within this bone.
The outer ear consists of the pinna, which is the external skin and cartilage on both sides of our heads that we think of when we hear the word “ear,” as well as the external auditory canal. The shape of the pinna is ideal to collect the sound waves, direct them down the ear canal, and vibrate the tympanic membrane, or eardrum. The eardrum separates the outer ear from the middle ear. In the middle ear, the eardrum’s vibrations move the Malleus (hammer), the Incus (anvil) and the Stapes (stirrup) bones of the middle ear, collectively known as the ossicles. With motion of the ossicles, the sound waves that first entered the ear canal have been converted to mechanical energy, and this energy is conducted toward the inner ear. Movement of the ossicles causes vibrations in the fluid of the cochlea, the hearing portion of the inner ear. As the cochlear fluid vibrates, it moves thousands of tiny hair-like nerve cells that line the cochlear walls, which serves to convert the mechanical energy of the ossicles into the requisite electrical nerve impulses. These impulses travel from the cochlea up the auditory nerve, where they are received and given meaning and relevance by the brain. The cone-shaped bone that forms the part of the skull immediately below and behind each ear is called the mastoid process. The internal ear structures and hearing processes are protected deep within this bone.
baby at 20 weeks, echocardiogram of human heart
Bats, dolphins, dogs, fish & insects all hear ultrasonic frequencies. Another well-known application of this same basic technique is sonar . In sonar, ultrasonic waves are emitted, and sensors detect the reflected portions of those waves. The sensors end up creating an image of any obstruction in their path, much like the image shown in Figure 14.6. Although sonar is best known as the way a submarine tracks ships and other submarines, the most efficient sonar known to humankind exists in the bat.
We have seen that the echo of a sound can be used to determine how far away something is, and we have also seen that we can use the Doppler shift of the echo to determine how fast something is going. It is therefore possible to create a "sound radar," and that is exactly what sonar is. Submarines and boats use sonar all the time. You could use the same principles with sound in the air, but sound in the air has a couple of problems: Sound doesn't travel very far -- maybe a mile at the most. Almost everyone can hear sounds, so a "sound radar" would definitely disturb the neighbors (you can eliminate most of this problem by using ultrasound instead of audible sound). Because the echo of the sound would be very faint, it is likely that it would be hard to detect. Radar therefore uses radio waves instead of sound. Radio waves travel far, are invisible to humans and are easy to detect even when they are faint.