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
Intensityvolume of sound (how loud, how soft)depends on energy (amplitude) of sound
wavemeasured in decibels (dB)
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
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.