Vibrations, Waves and Sound
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Vibrations, Waves and Sound. Unit 7: Vibrations, Waves & Sound Chapter 20: Sound. 20.1 Properties of Sound 20.2 Sound Waves 20.3 Sound, Perception, and Music. Key Question: What is sound and how do we hear it?. 20.1 Investigation: Sound and Hearing. Objectives:

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Vibrations waves and sound

Vibrations, Waves and Sound


Unit 7 vibrations waves sound chapter 20 sound

Unit 7: Vibrations, Waves & SoundChapter 20: Sound

  • 20.1 Properties of Sound

  • 20.2 Sound Waves

  • 20.3 Sound, Perception, and Music


20 1 investigation sound and hearing

Key Question:

What is sound and how do we hear it?

20.1 Investigation: Sound and Hearing

Objectives:

  • Identify the range of frequencies humans can hear.

  • Describe the how perception influences the sound humans hear.

  • Make and analyze a histogram of class data.


The frequency of sound

The frequency of sound

  • The pitch of a sound is how you hear and interpret its frequency.

  • A low-frequency sound has a low pitch.

  • A high-frequency sound has a high pitch.

Each person is saying “Hello”.


The frequency of sound1

The frequency of sound

  • Almost all the sounds you hear contain many frequencies at the same time.

  • Humans can generally hear frequencies between 20 Hz and 20,000 Hz.


The loudness of sound

The loudness of sound

  • The loudnessof a sound is measured in decibels (dB).

  • The decibelis a unit used to express relative differences in the loudness of sounds.


The loudness of sound1

The loudness of sound

  • Most sounds fall between 0 and 100 on the decibel scale, making it a very convenient number to understand and use.


The frequency of sound2

The frequency of sound

  • Sounds near 2,000 Hz seem louder than sounds of other frequencies, even at the same decibel level.

  • According to this curve, a 25 dB sound at 1,000 Hz sounds just as loud as an 40 dB sound at 100 Hz.


Decibels and amplitude

Decibels and amplitude

  • The amplitude of a sound increases ten times every 20-decibels.


The speed of sound

The speed of sound

  • The speed of sound in normal air is 343 meters per second (660 mi/hr).

  • Sound travels through most liquids and solids faster than through air.

  • Sound travels about five times faster in water, and about 18 times faster in steel.


The speed of sound1

The speed of sound

  • Objects that move faster than sound are called supersonic.

  • If you were on the ground watching a supersonic plane fly toward you, there would be silence.

The sound would be behind the plane, racing to catch up.


The speed of sound2

The speed of sound

  • A supersonic jet “squishes” the sound waves so that a cone-shaped shock waveforms where the waves “pile up” ahead of the plane.

  • In front of the shock wave there is total silence.


The speed of sound3

The speed of sound

  • Passenger jets are subsonicbecause they travel at speeds from 400 to 500 mi/hr.


The doppler effect

The Doppler effect

  • When the object is moving, the frequency will notbe the same to all listeners.

  • The shift in frequency caused by motion is called the Doppler effect.

  • You hear the Doppler effect when you hear a police or fire siren coming toward you, then going away from you.


Recording sound

Recording sound

  • Most of the music you listen to has been recorded in stereo.

  • The slight differences in how sound reaches your ears lets you know where sound is coming from.


Recording sound1

Recording sound

To record a sound you must store the pattern of vibrations in a way that can be replayed and be true to the original sound.

  • A microphone transforms a sound wave into an electrical signal with the same pattern of vibration.


Recording sound2

Recording sound

  • An “analog to digital converter” converts the electrical signal to digital values between 0 and 65,536.


Recording sound3

Recording sound

  • One second of compact-disc-quality sound is a list of 44,100 numbers which represents the amplitudes converted sounds.


Recording sound4

Recording sound

  • To play the sound back, the string of numbers is read by a laser and converted into electrical signals again by a second circuit which reverses the process of the previous circuit.


Recording sound5

Recording sound

  • The playback circuit converts the string of numbers back into an electrical signal.

  • The electrical signal is amplified to move the coil in a speaker and reproduce the sound.


Unit 7 vibrations waves sound chapter 20 sound1

Unit 7: Vibrations, Waves & SoundChapter 20: Sound

  • 20.1 Properties of Sound

  • 20.2 Sound Waves

  • 20.3 Sound, Perception, and Music


20 2 investigation properties of sound waves

Key Question:

Does sound behave like other waves?

20.2 Investigation: Properties of Sound Waves

Objectives:

  • Listen to beats and explain how the presence of beats is evidence that sound is a wave.

  • Create interference of sound waves and explain how the interference is evidence for the wave nature of sound.


What is a sound wave

What is a sound wave?

  • Sound waves are pressure waveswith alternating high and low pressure regions.

  • When they are pushed by the vibrations, it creates a layer of higher pressure which results in a traveling vibration of pressure.


Pressure and molecules

Pressure and molecules

  • At the same temperature and volume, higher pressure contains more molecules than lower pressure.

  • The speed of sound increases because collisions between atoms increase.

  • Therefore, if the pressure goes down, the speed of sound decreases.


The wavelength of sound

The wavelength of sound

  • The wavelength of sound in air is similar to the size of everyday objects.


The wavelength of sound1

The wavelength of sound

  • Wavelength is also important to sound.

  • Musical instruments use the wavelength of a sound to create different frequencies.


Reverberation

Reverberation

  • The reflected sound and direct sound from the musicians together create a multiple echo called reverberation.

  • The right amount of reverberation makes the sound seem livelier and richer.


Sound wave interactions

Sound wave interactions

  • Like other waves, sound waves can be reflected by hard surfaces and refracted as they pass from one material to another.

  • Diffraction causes sound waves to spread out through small openings.

  • Carpet and soft materials can absorb sound waves.


Ultrasound

Ultrasound

  • Ultrasound is high-frequency sound, often 100,000 Hz or more.

  • We cannot hear ultrasound, but it passes through the human body easily.

  • Medical ultrasound instruments use ultrasound waves to create images of the human body’s interior for diagnostic purposes.

The ultrasound image

above is a heart.


Standing waves in pipes

Standing waves in pipes

  • A panpipe makes music as sound resonates in tubes of different lengths.

  • The natural frequency of a pipe is proportional to its length.


Standing waves in pipes1

Standing waves in pipes

  • Because frequency and wavelength are inversely related, longer pipes have lower natural frequencies because they resonate at longer wavelengths.

  • A pipe that must vibrate at a frequency 2 times higher than another pipe must be 1/2 as long.

If the long pipe has a frequency of 528 Hz, what is the frequency of the short pipe?


Standing waves in pipes2

Standing waves in pipes

  • Blowing across the open end of a tube creates a standing wave inside the tube.

  • If we blow at just the right angle and we match the natural frequency of the material and the sound resonates (spreads).


Standing waves in pipes3

Standing waves in pipes

  • The open end of a pipe is an open boundary to a standing wave and makes an antinode.

  • The pipe resonates to a certain frequency when its length is one-fourth the wavelength of that frequency.


Wave speed and designing instruments

Wave speed and designing instruments

  • Sounds of different frequencies are made by standing waves.

  • The length of a vibrating system can be chosen so that it resonates at the frequency you want to hear.


Fourier s theorem

Fourier's theorem

Fourier’s theorem says any complex wave can be made from a sum of single frequency waves.


Sound spectrum

Sound spectrum

A complex wave is really a sum of component frequencies.

A complex wave can be made from a sum of single-frequency waves, each with its own frequency, amplitude, and phase.


Unit 7 vibrations waves sound chapter 20 sound2

Unit 7: Vibrations, Waves & SoundChapter 20: Sound

  • 20.1 Properties of Sound

  • 20.2 Sound Waves

  • 20.3 Sound, Perception, and Music


20 3 investigation sound as a wave

Key Question:

How can we observe sound as a wave?

How can we use the speed of sound and certain frequencies to build a basic instrument based on wavelength?

20.3 Investigation: Sound as a Wave

Objectives:

  • Explain how pitch is related to frequency and wavelength of a sound wave.

  • Determine the lengths of pipe required to produce sounds at certain frequencies at a specific speed of sound.

  • Construct a basic instrument from PVC pipe and use it to play musical notes.


Sound perception and music

Sound perception and music

  • When you hear a sound, the nerves in your ear respond to more than 15,000 different frequencies at once.

  • The brain makes sense of complex sound because the ear separates the sound into different frequencies.


Sound spectrum1

Sound spectrum

A frequency spectrum is a graph showing the different frequencies present in a sound.

Sound containing many frequencies has a wave form that is jagged and complicated.


Sonograms

Sonograms

  • More information is found in a sonogramwhich combines three sound variables:

    • frequency,

    • time, and

    • amplitude (loudness).


Sonograms1

Sonograms

Which letter represents a soft sound lasting 5 seconds?

What is it’s frequency?


How we hear sound

How we hear sound

  • The parts of the ear work together:

  • When the eardrum vibrates, three small bones transmit the vibrations to the cochlea.

  • The vibrations make waves inside the cochlea, which vibrates nerves in the spiral.

  • Each part of the spiral is sensitive to a different frequency.


Sound protection

Sound protection

  • Listening to loud sounds for a long time causes the hairs on the nerves in the cochlea to weaken or break off resulting in permanent damage.


Music

Music

  • The pitch of a sound is how high or low we hear its frequency.

  • Rhythm is a regular time pattern in a series of sounds.

  • Music is a combination of sound and rhythm that we find pleasant.


The musical scale

The musical scale

  • Most of the music you listen to is created from a pattern of frequencies called a musical scale.


Music and notes

Music and notes

  • Each frequency in the scale is called a note.

  • The range between any frequency and twice that frequency is called an octave.


Music and harmony

Music and harmony

  • Harmonyis the study of how sounds work together to create effects desired by the composer.

  • The tense, dramatic sound track of a horror movie is a vital part of the audience’s experience.

  • Harmony is based on the frequency relationships of the musical scale.


Beats

Beats

  • When two frequencies of sound are not exactly equal in value, the loudness of the total sound seems to oscillate or beat.


Echolocation and beats

Echolocation and beats

  • Bats navigate and find food using echolocation.

  • The beat frequency is proportional to how far the insect is from the bat.


Consonance and dissonance

Consonance and dissonance

  • When we hear more than one frequency of sound and the combination sounds pleasant, we call it consonance.

  • When the combination sounds unsettling, we call it dissonance.


Making sounds

Making sounds

  • The human voice is complex sound that starts in the larynx, at the top of your windpipe.

  • The sound is changed by passing over by expandable folds (vocal cords) and through openings in the throat and mouth.


Making sounds1

Making sounds

  • For a guitar in standard tuning, the heaviest string has a natural frequency of 82 Hz and the lightest a frequency of 330 Hz.

  • Tightening a string raises its natural frequency and loosening lowers it.


Harmonics and music

Harmonics and music

  • The same note sounds different when played on different instruments.

  • Suppose you compare the note C (262 Hz) played on a guitar and the same note played on a piano.

  • A single C note from a grand piano might include 20 or more different harmonics.


Harmonics and instruments

Harmonics and instruments

  • The variation comes from the harmonics.

  • The sound from an instrument is not a single pure frequency.


Hearing

Deafness is poorly understood in general.

For instance, there is a common misconception that deaf people live in a world of silence.

To understand the nature of deafness, first one has to understand the nature of hearing.

Hearing


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