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 grow back

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.42-47)

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.

Insert picture

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

1st overtone

2nd overtone

3rd overtone

4th overtone

5th overtone

6th 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

2nd overtone

Resulting sound wave

Sound Quality of Instruments

Instruments have different sound qualitiesbecause 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 lay across.

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 pitchesthicker 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.