The Nature of Sound

The Nature of SoundEQ: What are the properties of sound?An old riddle .If a tree falls in a forest, and no one hears it, does the tree make a sound?

What is sound?

Sound WavesTo a scientist, a tree makes a sound whether someone hears it or not.When a tree crashes down, the energy with which it strikes the ground causes a disturbance.Disturbances cause waves!

Sound WavesThe disturbance of the tree striking the ground causes the particles in the air and ground to vibrate.The vibrations create a sound wave as the energy travels through the two mediums.

Sound WavesSound is a disturbance that travels through a medium as a longitudinal wave

https://www.youtube.com/watch?v=kt1pTcfstC8

Sound Waves --- Making Sound WavesA sound wave begins with a vibration.https://www.youtube.com/watch?v=_0sWrqB2yTIWhen the gong was struck, it (the gong) vibrates rapidly.

Sound Waves --- Making Sound WavesThe gongs vibrations disturb nearby air particles.Each time the gong vibrates to the right, it pushes air particles together, creating a compression.When the gong vibrates to the left, the air particles bounce back and spread out, creating a rarefaction.The compressions and rarefactions travel through the air as longitudinal waveshttps://www.youtube.com/watch?v=ACeUO4ufx2I

Sound Waves --- How it travelsSound waves are mechanical waves, which means that they do carry energy through a medium without moving the particles of the medium along.

Sound Waves --- How it travelsEach particle of the medium vibrates as the disturbance (the wave) passes.When a disturbance reaches your ears, you hear the sound.

Sound Waves --- How it travelsA common medium for sound is air. (gas)But sound can travel through solids and liquids too.Ex: Knocking on a doorThe particles in the wood vibrate.The vibrations make sound waves that travel through the door.When the waves reach the other side of the door, they make sound waves in the air on the far side

The Interactions and Speed of Sound WavesEQ: What are the properties of sound?Interactions of Sound WavesLongitudinal sound waves interact with the surfaces that they contact and with each other.Sound waves reflect off objects, diffract through narrow openings and around barriers, they also interfere with each other.

Interactions of Sound Waves ---ReflectionSound waves may reflect when they hit a surface.A reflected sound is called an echo.In general, the harder and smoother the surface, the stronger the reflection will be.This is why a gym will have a more pronounced echo than a living room with carpet and upholstered furniture.

Interactions of Sound Waves ---DiffractionSound waves do not always travel in straight lines.Sound waves can move through barriers and openings in barriersThis is why you can hear people talking in a classroom in the hallway.Sound waves can bend around corners.This is why you can hear people talking in a hallway before you come around a corner.

Interactions of Sound Waves ---InterferenceSound waves may meet and interact with each other.This is called interference.When sound waves meet they can either join forces and the amplitude (strength) will rise.Constructive interferenceHowever, there can be dead spots in a room where the amplitude is reduced.Destructive Interference.

Reflection, Diffraction or Interference?

Find 3 pics of each (real life)16Reflection, Diffraction or Interference

Reflection, Diffraction or Interference

Reflection, Diffraction or Interference

Reflection, Diffraction or Interference

Reflection, Diffraction or Interference

The Speed of SoundLongitudinal sound waves travel at different speeds through different mediums.They travel fastest through solids, then liquids and slowest through gases (such as air)

The Speed of SoundThe speed of sound depends on the :

ElasticityDensity Temperature

Of the medium that the sound wave travels through.

The Speed of Sound--- ElasticityElasticity is the ability of a material to bounce back after being disturbed.A rubber band is more elastic than modeling clay it bounces back into shape, whereas the clay stays stretched.

The Speed of Sound--- ElasticityThe more elastic a medium, the faster the sound travels in it.Sounds can travel well in solids, which are usually more elastic than liquids or gases.This is because the particles of a solid do not move very much, so they bounce back and forth as compressions and rarefactions

The Speed of Sound--- DensityDensity is how much matter, or mass, there is in a given amount of space or volume.

The denser the medium, the more mass it has in a given volume.

The Speed of Sound--- DensitySound waves travel quicker in less dense mediums.The particles of a dense material simply do not move (or vibrate) as quickly as those of a less dense material.

The Speed of Sound--- TemperatureSound waves travel quicker at high temperatures than low temperatures.At low temperatures, particles move more slowly.This means they are more difficult to move, and then they return to their original positions more slowly as well

https://www.youtube.com/watch?v=Ude8pPjawKI

28FAST or SLOW?

FAST or SLOW?

FAST or SLOW?

Which travels faster?

Which travels faster?FROZEN POND

SolidMore elastic (because its a solid)

FAST or SLOW?

Properties of Sound EQ: What are the properties of sound?https://www.youtube.com/watch?v=mevjV5pcITchttps://www.youtube.com/watch?v=_ovMh2A3P5k35Properties of SoundSuppose that you and a friend are talking on the sidewalk and a noisy truck pulls up next to you and stops, leaving its motor on.What would you do?You might talk louder to be heard.You could lean in closer and speak into your friends ear.Or you might walk away to a quieter spot to finish your conversation.

Property 1 ---LoudnessLoudness is an important property of sound.Loudness describes your perception of the energy of a sound.In other words, loudness describes what you hear.

Property 1 ---LoudnessYou already know about loudness.You know that your voice is louder when you shout, vs. when you whisper.The closer you are to a sound, the louder it is.A whisper in your ear can be just as loud as a shout heard from down the road.

Property 1 ---LoudnessThe loudness of a sound depends on two factors:

The amount of energy it takes to make the sound

The distance from the source of the sound

Loudness--- Energy of a Sound SourceIn general, the greater the energy used to make a sound, the louder the sound. In the guitar demo you may have noticed this.The more energy used to pull the string back, the louder the sound when the string was let go.

Loudness --- Source of A SoundThis happened because the more energy you used to pull the string, the greater the amplitude of the strings vibration.A string vibrating with a large amplitude produces a sound wave with a large amplitude.The greater the amplitude, the louder it sounds

Loudness --- Distance From a Sound SourceLoudness increases the closer you are to a sound source.Just like ripples spreading out in circles after you have thrown a pebble in a puddle, sound waves spread out from their source.

Loudness --- Distance From a Sound SourceClose to a sound source, the sound wave covers a small area.As a wave travels from its source, it covers more area.The waves total energy, however, stays the same whether its close to source or far from it.

Loudness --- Distance From a Sound SourceThe closer the sound wave is to its source, the more energy it has in a given area.This is referred to as intensity.A sound wave with a greater intensity (or closer to its source) sounds louder than a source that is farther away (or less intense)

Add some example pictures who would hear the loudest sound?44Which sound would be louder?

Add pictures of cars passing, people talking, etc45Which sound would be louder?

Property 2 --- PitchPitch is another property of sound.Have you ever described someones voice as high-pitched or low-pitched?The pitch of a sound is a description of how high or low the sound seems to a person

47Property 2 --- PitchThe pitch of a sound wave you hear depends on the frequency of the sound wave.Frequency is the number of complete waves passing a certain point in a certain amount of time

Pitch and frequency video here

48Pitch and FrequencySound waves with a high frequency have a high pitch.

Sound waves with a low frequency have low pitch.

Pitch and FrequencyFrequency is measured in hertz (Hz)For example, a frequency of 50 Hz means 50 vibrations per second.A bass singer can produce frequencies lower than 80 Hz.A soprano voice can produce frequencies higher than 1,000 Hz.Most people can hear sounds with frequencies between 20 Hz and 20,000 Hz.

Changing PitchYou can change the pitch of your voice using your vocal cords.When using your voice, air from your lungs is forced up your trachea (windpipe).Air then rushes past your vocal cords, making them vibrate.This produces sound waves.Your vocal cords are able to vibrate more than 1,000 times per second

Changing PitchTo make the pitch of your voice higher or lower, you use muscles in your throat to stretch and relax your vocal cords.When your vocal cords stretch, they vibrate more quickly, and a higher frequency sound waves are created, producing a higher pitched sound.When your vocal cords relax, lower-frequency sound waves with lower pitches are producedhttps://www.youtube.com/watch?v=9MDn5GgyxyU

The Doppler EffectIf you listen carefully to the siren of a firetruck on its way to a fire, you may notice something:As the truck goes by you, the pitch of the siren drops.But the pitch of the siren stays constant to the firefighters on the truck.The sirens pitch changes only if it is moving toward or away from a listener.

Firetruck sounds 53The Doppler EffectThe Doppler Effect is a change in the frequency of a wave as its source moves in relation to an observer.

The Doppler EffectWhen a sound source moves, the frequency of the waves changes because the motion of the source adds to the motion of the waves.

Walking, vs. pushing someone in a chair. Tennis ball example 55