1. Chapter 21 What is Sound?
Section 1

2. What is sound?
Sound is a compressional wave which travels through the air through a series of compressions and rarefactions.

3. Sound Waves

4. Longitudinal Waves (Compression Waves)
What are mechanical waves?
Mechanical waves are waves which require a medium. A medium is a form of matter through which the wave travels (such as water, air, glass, etc.) Some examples of mechanical waves are : sound, ocean and seismic.
Longitudinal Waves (Compression Waves)
In a longitudinal wave the matter in the wave moves back and forth parallel to the direction of the wave

5. What are Seismic Waves?
An energy wave which vibrates through the earth’s crust as the crust bends or breaks. Seismic waves are exist as both transverse and compressional waves. Some travel through the earth and some travel across the earth’s surface.

6. Terms to Learn
Outer ear: acts as a funnel for sound waves. The pinna collects the sound waves and directs them into the ear canal.
Middle ear: there are 3 bones in the middle ear: the hammer, anvil and the stirrup-they act as levers to increase the amplitude of the vibrations.
Inner ear: this is where the vibrations created by sound are changed into electrical signals for the brain to interpret.

8. MAKING SOUND VS. DETECTING SOUND
What is the difference between making sound and detecting sound?
If a tree falls in the forest and no one is around to hear it, does it make a sound?
Sound was created, but it wasn’t detected.

9. HOW DO YOU DETECT SOUND?
Sound waves vibrate the eardrum.
This vibration makes the hammer, anvil and stirrup (bones in the ear) vibrate.
The vibrations of the stirrup make the entrance to the inner ear (the oval window) vibrate.

10. HOW DO YOU DETECT SOUND?
4. These vibrations create waves in the liquid inside the cochlea. The movement of this liquid causes the cilia (the tiny hairs inside the cochlea) to vibrate.
5. This bending of the cilia stimulates nerves which sends electric signals to the brain.

11. HEARING LOSS
The parts of the ear must work together for you to hear sounds.
If any of the parts is damaged or does not work properly, hearing loss or deafness may result.
Tinnitus is one of the most common types of hearing loss.

12. HEARING LOSS
Tinnitus results from long-term exposure to loud sound (i.e. concerts)
Loud sounds can cause damage to the hair cells and nerve endings in the cochlea
Damage to the cochlea or any part of the inner ear results in permanent hearing loss.