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Chapter 12, Section 1 The Nature of Sound

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Chapter 12, Section 1 The Nature of Sound. Sonic Boom. http://www.youtube.com/watch?v=-d9A2oq1N38. What causes sound? All sounds are created by something that vibrates Energy of these vibrations collides with nearby molecules of air and transfers this energy in all directions from the source

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slide1
Chapter 12, Section 1

The Nature of Sound

sonic boom
Sonic Boom

http://www.youtube.com/watch?v=-d9A2oq1N38

slide3
What causes sound?
  • All sounds are created by something that vibrates
  • Energy of these vibrations collides with nearby molecules of air and transfers this energy in all directions from the source
  • Sound is a compressional wave

A series of compressions

and rarefactions move

away from the source.

The result is a sound wave

http://www.brobproductions.com/bigstockphoto_Sound_Waves_1345039.jpg

slide4
Moving Through Mediums

Sound must have a medium (no sound in outer space!)

Sound can travel through any medium (solid, liquid, gas)

Speed of sound is determined by a medium’s density: the denser the medium, the faster the speed

Why?

The molecules in a dense medium are closer and transfer energy more rapidly

Air=437 m/s; Water=1498 m/s; Steel=5200 m/s

slide5
Moving Through Mediums

Careful: the speed of sound DOES NOT depend on loudness (amplitude)

Speed of sound is also determined by temperature

As temperature increases, the speed of sound increases

As temperature increases, molecules move faster

0°C Air=332 m/s; 20°C Air=344 m/s

slide6
Human Hearing

http://www.infj.ulst.ac.uk/~pnic/HumanEar/Andy%27s%20Stuff/MScProject/workingcode_Local/humanear.jpg

slide7
Human Hearing

Outer ear: gathers sound waves

Middle ear: amplifies (makes louder) sound waves

Inner ear: converts sound waves into nerve impulses

Brain: decodes and interprets nerve impulses

slide8
Outer Ear

Outer ear parts: auricle (pinna), ear canal, eardrum (tympanic membrane)

Auricle directs sound waves into the ear canal.

Ear canal (2-3 cm long) is a passageway to the eardrum.

Eardrum (0.1 mm thick) is a tough membrane that vibrates.

slide9
Human Hearing

http://www.infj.ulst.ac.uk/~pnic/HumanEar/Andy%27s%20Stuff/MScProject/workingcode_Local/humanear.jpg

slide10
Middle Ear

Middle ear parts: hammer (malleus), anvil (incus), stirrup (stapes), oval window

Eardrum vibrations cause the 3 tiny bones (hammer, anvil, stirrup) to vibrate.

These bones make a lever system that amplifies the sound wave.

The stirrup is connected to the oval window which transfers the vibration to the inner ear.

slide11
Human Hearing

http://www.infj.ulst.ac.uk/~pnic/HumanEar/Andy%27s%20Stuff/MScProject/workingcode_Local/humanear.jpg

slide12
Inner Ear

Inner ear parts: cochlea, hair cells

Oval window transfers vibrations to the cochlea, a spiral-shaped structure filled with fluid.

Within the cochlea’s fluid are tiny hair cells.

The hair cells vibrate and stimulate the auditory nerve that sends the information to the brain.

slide13
Human Hearing

http://www.infj.ulst.ac.uk/~pnic/HumanEar/Andy%27s%20Stuff/MScProject/workingcode_Local/humanear.jpg

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