Transcript Chapter 2: Sound

Chapter 2: Sound
Section 2: Properties of Sound
Do Now:
1. Copy homework
2. Cornell Notes
FQs: Why are sounds loud or soft?
Why are sounds high or low?
Two Main Properties of Sound
 Loudness:

Your perception of the energy of a sound
 Pitch:

The description of how high or low a sound
seems to a person
Loudness
 Your
perception of the energy of a sound
 Depends on two factors:
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
Energy used to make the sound
Distance from the source of the sound
 Energy


Pull back on a rubber band
Pull back even farther - louder
Loudness

Distance

Talk to person next to you

Lean in closer – louder

Close to source, wave covers small area

Wave travels away and covers larger area
Intensity: the
amount of energy a
sound wave carries
per second through
a unit area
Loudness

Measuring loudness


Sound
Unit: decibel (dB)
Each 10dB increase
represents a tenfold
increase in intensity
 30dB is ten TIMES louder
than 20dB
 30dB is 100 TIMES
louder than 10 dB
 Sounds louder than
100dB can damage your
hearing
Loudness
(dB)
Rustling leaves
10
Whisper
15-20
Very soft music
20-30
Normal
conversation
40-50
Heavy street
traffic
60-70
Loud music
90-100
Rock concert
110-120
Jackhammer
120
Jet plane takeoff
120-160
Pitch
 The
description of how high or low a
sound seems to a person
 Depends on the frequency of the wave
Pitch

Frequencies:
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Bass singer: lower than 80 Hz
Soprano singer: higher than 1,000 Hz
Most people can hear between 20 and 20,000 Hz
Above 20,000 = ultrasound
Below 20 = infrasound
How’s your hearing?
http://www.noiseaddicts.com/2009/03/can-you-hearthis-hearing-test/
Pitch

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Music uses specific pitches called notes
Change pitch using vocal cords, located in
larynx (voice box)
Vocal cords can vibrate more than 1,000 times
per second
Stretch and relax cords for different notes
Stretch – vibrate more quickly (higher frequency,
higher pitch)
Relax – vibrate more slowly (lower frequency,
lower pitch)
Same as guitar string
The Doppler Effect
 The
change in frequency of a wave as its
source moves in relation to an observer

 If
Austrian scientist Christian Doppler (18031853)
sound waves, heard as a change in pitch
 If light waves, seen as “red shift”
 Motion of source adds to motion of waves
Shock Waves
 Shock
waves are caused by the Doppler
effect
 The science behind shock waves is pretty
advanced and difficult to understand.
Maybe you could make it a journal
question….