Ch. 18 - Waves & Sound

II. The Nature of Sound Speed of Sound Human hearing Doppler effect Seeing with sound

What makes Sound?

1. Vibration: back and forth motion

a.There can not be sound if there is not any vibration

b.Most vibrations are too fast for you to see.

c.Vibrations require energy—sound is a form of energy.

How does Sound Travel?

2. When something vibrates molecules in the air crowd together, then spread apart, causing sound waves to travel away from the vibrating object

A. Speed of Sound

344 m/s in air at 20°CDepends on:

Type of medium• travels better through liquids and solids• can’t travel through a vacuum

Temperature of medium• travels faster at higher temps

Sound Reflection and Absorption

A. Reflected sound is called an echo.1. The vibrations are reflecting

back to you.B. Soft, air-filled objects absorb sound.

1. When sound is absorbed, you do not hear it because it is not reflected back to you.

B. Human Hearing

sound wave

vibrates ear drum

amplified by bones

converted to nerve impulses in cochlea

How do you hear sound? 1. Sound causes your eardrum to vibrate. The eardrum vibrates differently for each sound.

2. The bones of your ear begin to vibrate, beginning with the hammer, moves to the anvil, and finally the stirrup.

3. The sound energy passes to the inner ear. This causes the fluid in the cochlea to move.

4. The nerves then carry the message to the brain.

5. Your brain then tells you what the sound is.

http://www.youtube.com/watch?v=PeTriGTENoc

Once upon the time earhttp://www.youtube.com/watch?

v=UQV3ulHAPZM

Pitch

1. Pitch: how high or low a sound isa. The higher the pitch the more “squeezed”

together the waves are

b. The higher the pitch the higher the frequency

c. The lower the pitch the lower the frequency

B. Human Hearing

Pitchhuman range:

20 - 20,000 Hzultrasonic waves

subsonic waves

B. Human Hearing

Intensityvolume of sound (how loud, how soft)depends on energy (amplitude) of sound

wavemeasured in decibels (dB)

B. Human Hearing

7080

100110

120

40

1810

0

DECIBEL SCALE

C. Doppler Effect

Doppler Effectchange in wave frequency

caused by a moving wave source

moving toward you - pitch sounds higher

moving away from you - pitch sounds lower

Doppler effecthttp://www.youtube.com/watch?

v=h4OnBYrbCjY

C. Doppler Effect

Stationary source Moving source Supersonic source

same frequency in all directions

waves combine to produce a shock wave

called a sonic boom

higher frequency

lower frequency

D. Seeing with Sound

Ultrasonic waves - above 20,000 Hz

Medical Imaging SONAR“Sound Navigation Ranging”

2. Making Sound All sounds are made by vibrations. Humans make sound waves by using

their voice. The human voice is also made by

vibrations. The source of sound in humans is the

vocal cords. Vocal cords — 2 thin, elastic, bands of

tissue that vibrate to produce sound.

The 5 most annoying soundshttps://www.youtube.com/watch?

v=QakcwQHzPoYThe best sound in the worldhttps://www.youtube.com/watch?

v=oiYmkDSWFFw

Can silence actually existhttps://www.youtube.com/watch?

v=mXVGIb3bzHI

Why You Hate the Sound of Your Own Voicehttps://www.youtube.com/watch?

v=N970lhPK1hY

How do the vocal cords produce sound?1. Air from the lungs flows through the windpipe

and into the voice box (where the vocal cords are).

2. Then the air pushes the vocal cords apart making them vibrate.

3. The vibrations create a series of sound waves that exit through your mouth.

4. The change of shape of the vocal cords changes the sound and its pitch.

5. If you can’t talk because of a cold or laryngitis, it is because your vocal cords are swollen and inflamed.

Communication tools that use sound

Voice – allows you to communicate with others.

Morse Code – code for numbers and letters using sound

Sonar – a device that sends sound waves through water to measure or find something.

Animal soundsMusical instruments