1. Sound

2. If you recall, in order to produce sound a medium must vibrate.
Also sound waves are a compression or longitudinal wave. This wave is made up of compressions and rarefactions
Compression= when the coils of a spring a close together
Rarefaction= when the coils of a spring are spread apart
wavelength, 
rarefaction
compression

3. If that still confuses you then here is a molecular break down:
When sound travels though a medium there are alternating regions of high and low pressure. Compressions are high pressure areas where molecules are packed tightly together. Rarefactions are low pressure regions where the molecules are more spread out.
wavelength, 

4. Speed of Sound
The speed of sound depends on the substance of the medium and it’s state of mater (solid, liquid, or gas)
Medium
Speed of sound at room temp (m/s, 20°
Air
347
Cork
500
Water
1,498
Brick
3,650
Aluminum
4,877
Sonic Boom

5. Mach Numbers and Speed
Depending on temperature, sound travels around 374 m/s or 750 mph. This is referred to as Mach’s number or Mach 1.
Twice this speed or 758 m/s or 1500 mph is called Mach 2 which is about the maximum speed for the F-22 Raptor.
Speed Racer drives a car called “The Mach 5”, which implies it goes 5 times the speed of sound.

6. The speed of sound is affected by temperature.
If you recall we have defined as the average kinetic energy of particles in an object.
The faster the particles are moving in a medium before creating a sound allows for faster transfer of energy from the sound wave.

7. Human Hearing
Human hearing was designed to work in the slower medium of air.
It uses your ears to turn compressional waves into meaning.
It occurs in 4 stages
First, the ear gathers the compressional waves
Second, the ear amplifies the waves.
Third, the amplified waves are converted into nerve impulses
Fourth, the nerve impulse travels to the brain where it is then decoded and interpreted.

8. Sections of the ear
Outer ear—visible part, this is where sound is first gathered, directs it down the ear canal to the eardrum.

9. Middle ear—contains the ossicles of the ear.
As the eardrum vibrates, then it causes vibrations in the small bones
The bones are the Malleus (hammer), Incus(anvil), and the stapes (stirrup)
The stapes vibrates the cochlea

10. Inner ear—consists of the cochlea, which is the spiral-shaped structure that is filled with liquid and contains tiny hair cells
When these hairs vibrate they send a signal to the auditory nerve which takes the signal to the brain for decoding and interpretation.
When a person experiences hearing loss is is usually because these hairs have become damaged and can’t vibrate any more

11. Content Check What are two things that affect the speed of sound?
What makes an ear drum vibrate?
Why does sound speed up when temperature increases?
Why must there be a medium for sound to exit?
Some people hear ringing in their ears, called tinnitus, even in the absence of sound. Why do you think this occurs?