1. Chapter 10
Sound

2. Sounds are caused by waves
Longitudinal Waves
The direction of the wave is also the direction of the particle movement
Travels through air
It is a mechanical wave
Needs matter to travel through
Energy is transferred when one particle collides with another
In the compression part of the wave, the particles are pushed close together
In the rarefaction part, the particles are further apart

4. Mediums Sound can travel through any medium
Air is the most obvious
In water, sound travels faster but is less clear
In solids, sound travels even faster
Recall that the different forms of matter have properties based on how the atoms are arranged

5. Where can’t sound be transmitted?
In the absence of matter, sound waves can not transfer energy.
This means that, in space, there can be no sound
Astronauts must use transmission equipment to talk to, and hear one another

6. Speed of Sound Sound travels at different speeds in different mediums
Air, liquids, solids
It also travels different speeds through each medium depending on the temperature, density, and elasticity of the matter

7. Temperature
As the temperature of any matter increases the particles in the matter move faster.
More collisions=more energy transfer=more heat
This increase in collisions also affects the transfer of sound waves
If particles are moving faster, they are bumping into each other more, and therefore transferring sound faster
If the matter is cooled, the particles move slower and sound is slower to transfer.
The speed of sound in air at room temperature (21 degrees C) is 346m/s
At 0 degrees C, the speed falls to 330 m/s

8. Density Density=mass/volume
If the particles in an object are closer together, the object will be more dense
In a dense object, particles bump into one another more often
This will transfer energy (sound) more quickly

9. Elasticity
Elasticity-the tendency of an object to rebound to its original state when deformed
Rubber bands have high elasticity
Paper does not (It stays deformed)
Sound waves travel more quickly through elastic objects
Solids tend to be more elastic (air and liquids do not stretch)

10. How do we hear sound?
Human ears have the ability to collect sound waves and transfer signals to the brain
The brain reads the signals
There are 3 sections of the ear
The outer ear
The middle ear
The inner ear

11. The outer ear
The part that you see (cartilage) along with the ear canal and Tympanic membrane
The shape of the ear helps gather sound waves and direct them into the ear canal.
The ear canal is 2-3cm long, and about 0.7 cm in diameter
The sound waves travel down this canal until they reach the ear drum
The Tympanic membrane (a.k.a. Ear Drum) is a tough membrane that vibrates when sound waves reach it
It is about 0.1 mm thick

13. Middle Ear
As the Tympanic Membrane vibrates, it passes the sound waves into the middle ear
Consists of 3 bones
Malleus (hammer)
Incus (Anvil)
Stapes (Stirrup)
As these bones vibrate, they amplify the sound waves
The Stapes is connected to the oval window, and causes it to vibrate

14. The inner ear Fluid-filled portion of the ear
The oval window vibrates, transferring the sound waves to fluid waves that travel through the inner ear
The inner ear contains the cochlea
Filled with fluid and contains tiny hair cells, which transmit signals to the auditory nerve (cochlear nerve), through which they travel to the brain
The brain reads the signals and deciphers them

16. Hearing loss Damage to the ears can result in hearing loss
Loud noises can damage or destroy the hair cells in the cochlea
These do not grow back and cannot be replaced
Research is looking into ways to fix this
The easiest way to avoid hearing loss is to refrain from loud sounds

17. Amplitude of Longitudinal Wave
Amplitude is the amount of disturbance of a wave
I.E. How much the matter is disturbed by the wave
In a longitudinal wave, it is how close the particles are pushed together
Higher amplitude=more compressed
This occurs when more energy is added
Amplitude is related to intensity

18. Intensity The amount of energy that passes a point in a given time
Measured in decibels (dB)
If you increase the volume of a sound-emitting device, the amplitude increases, as does the intensity
More energy is carried past a point in a given amount of time
The opposite happens if you decrease the volume
If intensity is higher, the sound travels further because it has more energy

19. Distance and Intensity
Sound does not travel forever
Eventually, the energy is lost to the environment as it converts to other forms of energy (thermal energy)
Also, the wave spreads out
This spreads the energy out, lowering the intensity until the sound is no longer audible

20. Loudness The human perception of sound volume Depends on intensity
Higher volumes (i.e. louder sounds) have more energy and cause your eardrum to vibrate farther back and forth
This is what you perceive to be “LOUD!”
Lower volumes cause the eardrum to vibrate less
This is what you perceive to be “quiet”

21. The Decibel Scale The unit of intensity is the decibel (dB)
Defined as 1/10 of a bel
A unit named after Alexander Graham Bell, inventor of the telephone
The bel was too large of a unit, so the decibel was used instead
Deci=1/10
It is a logarithmic scale
Based on Powers of 10 of the number of bels
Going from 10 dB (1 B) to 20 dB (2 B) results in 10x the intensity
Going from 10 dB (1 B) to 30 dB (3 B) results in 102 =100x the intensity

22. Example Problem
How much more intensity is there in the sound of normal conversation (60 dB) than in whispered conversation (20 bB)?
60 dB-20 dB=40 dB
40 dB=4 B
104=10,000 times as much intensity

23. You Try It
The intensity of the classroom on a typical work day is 90 dB. I ask that it be brought to 30 dB. How much more intense is the sound than it should be?
1,000,000 times as intense...

25. The Decibel Scale The lowest (theoretically) that we can hear is 0 dB
Sound can be less intense, and other organisms can hear it, but we cannot
The pain threshold for humans is about 120 dB
Sustained sound at 90 or more dB can cause hearing loss
Ear protection is recommended if exposed more than 15 minutes per day
Even seconds of 120+ dB sounds can cause hearing loss

26. Pitch How high or low a sound seems to be Related to frequency
Frequency is the number of waves that pass a point each second
As frequency increases, the pitch gets higher
As frequency decreases, pitch gets lower
The pitch/frequency a human can hear varies, and decreases with age. You can probably hear from 20 Hz to 20,000 Hz
Other animals can hear sound at much higher frequencies
Dogs can hear to 35,000 Hz, and bats to 100,000 Hz

27. The Doppler Effect
The change in wave frequency due to the movement of the source of the wave or the observer
When an object is emitting a sound and moving towards an observer, the sound waves are pushed closer together, increasing the frequency of the sound
As the object moves away from a stationary observer, the waves are pulled apart, decreasing the frequency of the sound
Also occurs in light, as will be discussed next chapter

28. Noise vs. Music Noise has random patterns and pitches
Music is any collection of sounds that are deliberately used in a regular pattern

29. Natural Frequencies and Resonance
All objects have natural/fundamental frequencies
Particular set of frequencies at which an object vibrates
Musical instruments use these to create the sounds that we know
The sounds created by instruments are amplified by resonance
The air vibrates as the instrument is played
This makes the sound louder

30. Beats Occur when different frequencies combine
Sound like little breaks in the sounds
This is a type of interference

31. Using Sound: Acoustics
The study of sound
The size, shape, and materials present in a room can greatly affect sound quality
Acoustic engineers study these to determine the best way to make effective concert halls

32. Echolocation
Some animals use sound waves to locate objects

33. Sonar
A system that uses underwater reflection of sound waves to find things

34. Ultrasound Using sound waves that cannot be heard by humans
Above 20,000 Hz
Used in medicine to examine body parts
Including fetuses in the uterus