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 ear drum
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 ear drum (a.k.a. Tympanic membrane) 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 fibrates, 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 music