Unit 10 – Sound
Unit Big Idea: Sound waves transfer energy through vibrations.
Lesson 1 – Sound Waves and Hearing
Essential Question: What is sound?
By the end of this lesson, you should be able to describe what sound is, identify its properties, and explain
how humans hear it.
- vibration – complete back-and-forth motion of an object
- vibrations in the air are interpreted as sound in your brain
- all sounds are created by vibrations
- sound wave – longitudinal wave that’s caused by vibrations and travel through a medium
- longitudinal wave – particles of a medium vibrate in the same direction that the wave travels
- also called compression waves
- made of compressions and rarefactions
- compression – where the particles are close together
- rarefactions – where the particles are spread apart
- as waves travel through a medium, the particles are compressed together then spread apart
- sound waves travel in all directions away from their source – only if in a medium
- sound waves travel by disturbing the particles in a medium (matter of solids,
liquids, or gases)
- the particles in the medium do not travel with sound waves
- the particles of the medium vibrate back and forth along the path the wound wave travels
- sound waves can travel through air, water, glass, metal, etc
- sound waves won’t travel through a vacuum, like outer space, because there are no particles to
vibrate back and forth
- humans detect sound in the ear
- ear acts as a funnel for sound waves down from the outer ear into the inner ear
- the ear drum, located at the end of the ear canal, vibrates with the sound
- the vibrating ear drum transfers the vibrations (energy) to 3 tiny bones, called the hammer, anvil,
and stirrup, in the middle ear
- these 3 bones carry the vibrations to the oval window, which is the entrance to the inner ear
- the vibrations go from the oval window through the fluid in the cochlea that is covered in tiny
hairs
- the vibrations of the sound waves cause the cochlea fluid to move and bend the hairs
- the bending hairs in the cochlea makes the nerve cells send electrical signals to the brain through
the auditory nerve
- the electrical signals are sent to the brain where the sounds are interpreted
- pitch - how high or low you think a sound is
- the pitch you hear depends on your ear’s sensitivity to pitches over a wide range
- pitch depends on the frequency and wavelength of a sound wave
- the higher the frequency of the wave, the shorter its wavelength & the higher its pitch
- high-frequency waves have shorter wavelengths and produce high- pitched sounds
- low-frequency waves have longer wavelengths and produce
low-pitched sounds
- loudness - measure of how well a sound can be heard
- amplitude – maximum distance that the particles of a wave’s medium vibrate from their midline or rest
position
- measure of how much energy a sound wave carries or the wave’s intensity
- when you strike a drum softly, you get a low amplitude and a soft sound
- when you strike a drum harder, you get a higher amplitude and a louder sound
- the greater the amplitude, the louder the sound; the smaller the amplitude, the softer the sound
- amplifiers can be used to increase the loudness of the sound wave
- the amplifier receives the sound signal in the form of an electric current and increases the waves
amplitude to make the sound louder
- decibel (dB) – unit used to express loudness
- the softest sound humans can hear is 0 decibels (dB)
- sounds that are 120 dB or higher can be painful and can cause hearing loss with short exposure
- loud sounds that are not painful can cause hearing damage or loss if exposed to them over long
periods of time
- loud sounds can damage the hairs in the cochlea that create the electrical signals that are sent to
the brain – there hairs NEVER grow back
- to protect your hearing:
- use earplugs to block loud sounds
- lower the volume when using earbuds
- move away from the speaker that is playing loud music
- Doppler effect - change in the observed frequency of a wave when the sound source, the observer, or
both are moving
- when the source of the sound and the observer are moving closer together, the sound waves are
closer together – have a higher frequency and a higher pitch
- when the source of the sound and the observer are moving apart, the sound waves are farther
apart from each other – have a lower frequency and a lower pitch
- the Doppler effect is being used to explain what is happening in the universe
- the stars are red shifted away from Earth; this means that they are moving away from Earth and is used
as proof that the universe is still expanding today
Lesson 2 – Interactions of Sound Waves
Essential Question: How do sound waves travel and interact?
By the end of this lesson, you should be able to describe how sound waves interact, and how they can
cause echoes and sonic booms.
- sound waves travel more slowly than light waves
- this is why you hear the thunder after you see lightning
- 2 factors affect the speed of sound
- type of medium sound is traveling through
- sound travels fastest in solids and slowest in gases
- sound travels fastest in solids because solids are denser and the particles are packed
closer together, allowing them to transfer the energy of the sound wave more quickly
- temperature of the medium
- sound travels faster at higher temperatures than lower temperatures
- the higher the temperature of the medium, the faster the particles are moving in it and the
faster they will bump into each other and transfer the energy of the sound wave
- knowing these two factors allows you to predict the speed of sound
- sound waves react differently with different solid mediums / barriers
- waves can bounce back off a solid medium (echo)
- barriers can reflect a sound wave
- reflection –bouncing back of a wave when the wave hits a barrier
- strength of the reflected sound wave depends on the reflecting surface
- sound waves reflect best off smooth, hard surfaces, like bare walls, ceiling, and floors
- when furniture, carpets, and curtains are added to a room, the sound is softer
- waves can be absorbed into the solid medium and give their energy to the medium
- a rough wall (and acoustic tiles) absorbs sound better than a smooth wall
- soft materials (like fabrics and carpets) absorb sound better than hard materials
- matter or mediums that absorb sound waves reduce the echo or bouncing back of the
sound wave
- waves can be transmitted through the solid medium and carry on out the other side
- echo – reflected sound wave
- strength depends on the reflecting surface
- can be reduced by soft materials, and rough or irregular surfaces
- rough and irregular surfaces reduce echoes by scattering the sound waves
- echolocation – use of reflected sound waves to find objects
- some animals, like dolphins, bats, and whales, use echoes to hunt for food and to find objects in
their paths
- animals are able to tell how far away something is by how long it takes the sound waves to echo
back to them
- sonar - (Sound Navigation And Ranging) type of electronic echolocation that uses echoes to locate
object underwater
- interference - happens with two or more waves overlap and combine to form one wave
- in music, beats happen when two sound waves of nearly equal frequencies interfere – the wave
frequencies are not quite equal and form a repeating pattern of constructive and destructive
interference that sounds loud then soft over and over again
- constructive interference – waves overlap and combine to form a larger wave with a higher amplitude
- the higher amplitude creates a louder sound
- this can make very loud sounds, like a sonic boom
- destructive interference – waves combine to and cancel each other out to form a smaller wave with a
lower amplitude
- the sound is softer since the waves interfere with each other and the amplitude is lower
- some noise canceling headphones use destructive interference to filter out the noise around you
- sonic boom – sound produced when jet airplanes travel faster than the speed of the sound they are
making
- sonic booms from low flying planes can break windows
- because the jets are flying faster than the sound they create, the sound waves pile up in front of
them due to constructive interference and the jet has to “break through” this barrier
- sound barrier - high-pressure area in front of fast moving jet planes
- supersonic speed – speeds faster than the speed of sound
- resonance – happens when a sound wave matches the natural frequency of an object and causes the
object to vibrate
- the air in a seashell vibrates a certain frequencies because of the shape of the shell – this is how
you hear “the ocean” in a seashell
- natural frequencies or resonance frequencies – the frequency, or set of frequencies that an object has
when they vibrate
- all object have natural frequencies they vibrate at
- resonance happens whenever an object is vibrating at or near the natural frequency of a second
object – it causes the second object to vibrate
- an opera singer can sing a note that vibrates near the natural frequency of glass and breaks the
glass
- you feel the bass of loud music because it is resonating in your body
- a vibrating tuning fork can cause another object to vibrate if the tuning fork is near the natural
frequency of the other object
- resonance in musical instruments
- wind instruments
- you blow air into the mouth piece and across the reed to create vibrations
- the vibrations get louder when it forms a standing wave inside the instrument
- standing wave – pattern of vibration that looks like a wave that is standing still
- resonance occurs when standing waves are formed
- waves and reflected waves of the same frequency go back and forth in standing waves
inside the instrument
- string instruments
- strings are moved to create vibrations that make a standing wave
- sound waves get louder as they move through the body of the instrument
- resonance in man-made structures
- resonance can happen in buildings, towers, and bridges
- if wind or sounds near these structure are the same frequency as the structure, the building,
tower, or bridge will collapse
Lesson 3 – Sound Technology
Essential Question: How does sound technology work?
By the end of this lesson, you should be able to describe how sound technology is used to extend human
senses.
- echolocation – use of echoes, or reflected sound waves to find objects
- ultrasound - sound waves that have frequencies greater than 20,000 Hz
- used by animals that hunt or move around using echolocation
- these frequencies are too high for humans to hear
- allows animals to tell how far away an object is by the time it takes for the ultrasonic waves to
bounce off an object and return to them or echo back
- sonar - system that uses sound waves to determine the location of objects or to communicate
- visually impaired people can use sonar technology to navigate
- used to find shipwrecks, to avoid icebergs, to find fish, and to map the ocean floor
- an instrument on the ship sends out an ultrasonic wave and detects the echoes that are reflected
back
- ultrasounds are used in medicine too
- ultrasound are used to see inside a person’s body to detect tumors and other problems with
organs
- ultrasounds are not harmful to the human body cells, unlike X-rays; and don’t harm unborn
babies
- ultrasounds are used to see the development of a fetus, unborn baby, and to see the gender of the
baby as well
- sound waves, like all waves, lose energy as they travel away from the source
- the further away you are from the sound, the quieter it will be; the closer you are to the sound,
the louder it will be
- telephones and sound waves
- phones change sound waves into other types of signals that can be sent over long distances
- phones can also change the signals they receive back into sound waves that you hear
- the microphones in all phones change sound waves from your voice into electrical signals that
are transmitted over telephone lines where the receiver changes them back into sound waves for
you to hear
- cordless phones change the electrical signal into radio waves and transmit them to the base that
sends them over the telephone lines as electrical signals
- computers send the telephone’s electrical signals over the wires to the correct location
- cell phones use radio waves to send signals to cell phone towers that transfer the signals to
underground phone cables
- once sound waves lose their energy, they are gone forever
- people make recordings of sound waves (speeches, music, etc) to preserve the information
- Thomas Edison invented the phonograph, which could record and play back sound
- later sound waves were stored in the grooves of records
- today most sound waves are stored on compact discs (CDs) or computer files
- compact discs (CDs)
- information is stored by pressing microscopic pits into the plastic of the disc
- the pits and lands (spaces between the pits) form a spiral pattern on the CD
- the closer together the pits are the more information can be stored on the CD
- the pattern stores digital sounds as 1s and 0s that are used to recreate sound waves
- CD player uses light to read the information stored on the CD
- the plastic layer of a CD is coated with a thin layer of shiny aluminum
- the light from a laser reflects off the shiny surface as the CD rotates
- the pattern on the CD surface produces a pattern of light and dark reflected light
- the detector changes this pattern into an electrical signal
- the CD player then changes the electrical signal back into sound waves for you to hear
- computers
- sound is also stored as digital files in a computer
- digital sound files, like MP3 files, can store a large amount of sound information
- to record sound as a computer file, the original sound is first changed into an electrical signal
- the electrical signal is stored as a digital file on the computer’s hard drive
- the digital file is a series of 1s and 0s, similar to the pattern stored in a CD
- software reads the digital files and produces an electrical signal that is sent to the speakers
- the speakers change the signal back into sound waves
- MP3 players store and play back sound files in a similar way as larger computers