Presentation on theme: "Chapter 4 Bellringers Tuesday 10/27/09 How do you use sound everyday? Alarm clock or parent’s voice to wake you Cell phone ringing Television School bus."— Presentation transcript:
Chapter 4 Bellringers Tuesday 10/27/09 How do you use sound everyday? Alarm clock or parent’s voice to wake you Cell phone ringing Television School bus horn Dog barking to let you know he needs out
Ch. 4 The Nature of Sound Section 4-1 What is Sound? (Pgs. 30 – 35) Characteristics of all sound waves 1. All sounds are created by vibrations – back and forth movements of an object Sound from a speaker As speaker moves outwards, it pushes air particles together Creates a compression
When speaker moves back inwards, the air particles are no longer crowded. Creates a rarefaction Previous compression is still moving outward through the air particles. For each vibration of the speaker, a compression and rarefaction is formed
Compressions and rarefactions made by the vibrations of a tuning fork
2. All sound waves are longitudinal waves Particles vibrate back and forth in same direction as the sound waves Sound waves moves out in all directions from a source Air particles also vibrate outwards in all directions Air particles do not move with the sound waves
3. All sound waves are mechanical waves Sound waves must have a medium A medium is a substance through which a wave travels Some sound wave media are air, water, glass, and metal In a vacuum, there are no medium particles to vibrate and no sound is produced
Wednesday 10/28/09 What are the three characteristics of all sound waves? All sound waves are created by vibrations All sound waves are longitudinal waves All sound waves are mechanical waves
How you create sound Larynx – organ in your throat that contains vocal cords Vocal cords are thin strips of muscle They form a V-shaped opening in the airway When you speak, air is forced up through the larynx, causing vocal cords to vibrate
How you detect sound Outer Ear Pinna collects sound waves. Ear canal carries sound waves towards the middle ear.
Middle Ear Sound waves coming from ear canal vibrate eardrum Eardrum is a stretched membrane
Behind the eardrum are three tiny bones (HAS) Hammer Anvil Stirrup Hammer is pushed up against the eardrum Anvil is connected to hammer, and stirrup is connected to anvil The job of these bones is to increase vibrations
Middle ear cavity has an eustachian tube attached Eustachian tube opens into the throat Allows pressure to be released from the middle ear cavity
Inner Ear (Cochlea) Stirrup is up against an opening in the cochlea called the oval window Stirrup vibrates the oval window creating waves in the liquid in the cochlea Movement of liquid causes tiny hairs in the cochlea to bend These hairs are attached to nerves that send signals to the brain, which interprets those signals into sound
Thursday 10/29/09 What two things make up the outer ear? Pinna and ear canal What is the job of the bones in the middle ear? Increase vibrations What two things are inside the cochlea? Liquid and tiny hairs What causes signals to be sent to the brain from the ear? The bending of the hairs in the cochlea
Making a Sound vs. Hearing Sound When a tree falls, it and the ground vibrate It causes compressions and rarefactions in the air creating a sound If no one is around, vibrations are still being made They are just not being detected by anyone
Hearing Loss and Deafness Can be caused if any part of the ear is damaged and does not work. Tinnitus- hearing loss caused by long-term exposure to loud sounds Causes damage to the hair in the cochlea, which will not growback Missing cochlea hair Hole in eardrum
Protecting Your Hearing 1. Block out loud sounds with earplugs. 2. Use headphones at a low volume. 3. Move away from loud speakers.
Section 4-2: Properties of Sounds Speed of Sound Speed of sound depends on the medium the sound is traveling through Two different sounds will travel the same speed through the same medium Does NOT matter how loud they are A loud sound and a soft sound will both travel the same speed through the same medium
What changes the speed of sound? 1. Temperature The cooler the medium, the slower the sound. When a medium’s particles are cooler, they do not vibrate as fast. Energy is not passed from particle to particle as quickly. When the first pilot flew faster than the speed of sound, he flew high in the sky
This higher up he went, the colder the air became As a result sound did not travel as fast If he would have flown lower, his plane would have had to gone faster because the sound would have traveled faster in the warmer air
2. Different media Sound travels fastest in solids. Solid’s particles are closer together than in liquid and gases Energy is passed quicker in solids Sound travels slowest in gases because particles are furthest apart in gases
When does sound travel the fastest? Sound travels fastest through a warm solid medium Sound travels slowest through a cold gas medium
Monday 11/2/09 How does temperature effect sound? The lower the temp, the slower the vibrations of particles so sound is passed slowly from particle to particle How do different media effect sound? Solid particles are closest together so sound is passed quicker Gas particles are furthest apart so sound is passed slower
Pitch and Frequency Pitch- how high or low a sound is. Pitch depends on the frequency- number of waves per second Higher frequency (more waves per second) = higher pitch sound Lower frequency (less waves per second) = lower pitch sound
Humans can hear sounds from 20 to 20,000 hertz. Items such as a dog whistle are higher than 20,000 hertz and cannot be heard by humans. Ultrasonic – frequencies that are too high for humans to hear.
Doppler Effect- observed change in frequency when either the sound source or observer is moving. As a police siren travels towards an observer, it is traveling in the same direction as the sound waves moving towards the observer As a result, compressions and rarefactions are closer together Sound of the siren is higher
As police siren passes observer, it is moving in opposite direction of sound waves traveling towards the observer. As a result, compression and rarefactions are spread further apart. The sound of siren is lower.
Tuesday 11/3/09 What is the Doppler effect? Observed change in pitch of a moving sound source What determines the pitch of a sound? The frequency of the sound wave What do we call sounds that are too high in frequency for humans to hear? Ultrasonic
Loudness and Amplitude Loudness- measure of how well a sound is heard. When a drum is hit hard, the skin of the drum moves a large amount As a result the amplitude of the vibration created in the air is large Increasing the amplitude of the wave makes the sound louder. Sound waves with smaller amplitudes are softer sounds.
Measuring Loudness Decibel – unit for measuring loudness Softest sounds that a human can hear are around 0 decibels. Sounds at 120 decibels and higher are painful.
“Seeing” sound waves Oscilloscope- can graph representations of sound waves. Shows them as transverse waves instead of longitudinal waves Allows amplitude and frequency to be seen easier. Crests represent compressions Troughs represent rarefactions
Section 4-3 Interactions of Sound Waves (Pg ) Reflection of Sound Waves Reflection- bouncing back of a sound after hitting a barrier Echo - the reflection of a sound wave.
The strength of the echo depends on the surface the wave reflects off of. Waves reflect best off of hard, smooth surfaces Ex. Gym walls Soft, rough surfaces absorb sounds instead of reflecting them Ex. Auditorium walls
Echolocation- the use of reflected sound waves to locate objects. Dolphins and bats use echolocation Can determine the distance of object by how long it takes for the reflected waves to return
Using the Doppler effect lets them know if object is moving towards or away from them If reflected sound waves have a higher frequency object is moving towards them If moving away, reflected sound waves will have a lower frequency
Monday 11/9/09 What determines the strength of a reflected sound wave? The surface it reflects off of What is echolocation? The use of reflected sound waves to locate things
Human use of echolocation SONAR (SOund Navigation And Ranging) Ultrasonic waves are used because they have short wavelengths The short wavelengths allow a clearer picture be given of the object they reflected off of. Waves do not diffract around the object
Ultrasounds Medical procedures that uses echoes to see inside human bodies Uses frequencies of 1 million to 10 million hertz As a result, the wavelengths are short and great detail can be seen
Interference of Sound Waves Interference- overlapping of waves. Constructive Interference – two compressions or two rarefactions overlapping Amplitude increases Causes sound to be louder Destructive Interference – a compression and rarefaction overlapping Decreases amplitude Causes sound to be softer
Interference and the Sound Barrier As a jet speeds up, sound waves in front of the jet get closer together. Once the jet reaches the speed of sound, all the sound waves will build up on top of each in front of the jet. Jet must overcome the pressure of the compressed waves in front of it known as the sound barrier.
Once the jet passes the compressed waves, the sound waves will trail off behind the jet. Forms a cone of sound waves behind the jet The edges of these sound waves combine constructively to form a shock wave Amplitude has increased so sound is loud You hear a sonic boom when the shock wave reaches your ears, not when jet breaks the sound barrier.
Tuesday 11/10/09 Why are high frequencies used in echolocation? Short wavelengths allow a clear, more detailed picture How do sound waves interact with each other after a jet breaks the sound barrier? The waves overlap constructively and produce a loud sound
Interference and Standing Waves When a guitar string is plucked, a standing wave is formed. Caused by the interference of newly produced waves and reflected waves Constructive interference causes the part of a standing wave that always appears to have amplitude Destructive causes part that always appears to be in rest position
Resonant Frequencies- frequencies at which standing waves are formed Fundamental Frequency- frequency consisting of only one standing wave. Overtones- frequencies consisting of more than one standing wave
Fundamental 1 st overtone 2 nd overtone 3 rd overtone 4 th overtone 5 th overtone 6 th overtone
Resonance Resonance- when one object vibrating at the resonant frequency of another object causes that object to vibrate. Strike a tuning fork that is producing a resonant frequency If held near a guitar sting that has the same resonant frequency, guitar string will vibrate.
Resonance in Instruments Wind instruments create standing waves inside String instruments have hollow bodies so standing waves enter the body Cause the body of the instruments to vibrate with standing waves Causes sound to amplify
Section 4-4 Sound Quality (Pgs. 48 – 51) Sound Quality Why do two different instruments playing the same note sound different? Each instrument’s note comes from combining several standing waves: the fundamental and some overtones Each standing wave has a different pitch Sound Quality – the result of mixing different pitches (or standing waves) through interference
Fundamental frequency 2 nd overtone Resulting sound wave
Sound Quality of Instruments Instruments have different sound qualities because they mix different standing waves Instruments mix different standing waves because they are all built different All produce sounds by vibrations However, they vary in the part of the instrument that vibrates and how vibrations are made
String Instruments Sound is made when strings are plucked Have strings of different thickness. Thicker strings have a lower pitch. Thinner strings have a higher pitch Pitch can be changed by changing the length of string Push the string down on the neck of the instrument to make it shorter Shorter strings = higher pitch
Some string instruments have a bridge that the strings layacross. So when strings vibrate, the bridge vibrates, and the body of the instrument vibrates Resonance of the body and air inside the body makes a louder sound
Thursday 11/12/09 How does an instrument produce a note? By combining different standing waves Other than their sizes, how else do instruments differ? By what vibrates and how those vibrations are produced Why are the strings different sizes on a string instrument? thinner strings give higher pitches thicker strings give lower pitches
Wind Instruments Vibrations are created by blowing into one end of the instrument This creates a standing wave inside the instrument Change pitch by changing the length of the air column (the inside of the instrument) This is done by opening and closing valves and holes The longer the column, the lower the pitch
Percussion Drums, bells, and cymbals All vibrate when hit Different pitches come from the different sizes The larger percussion instrument, the lower the pitch
Music or Noise? Noise- any sound that is a random mix of frequencies Most sounds we hear are noise Music has a repeating pattern of frequencies.