Sound
What is Sound?
 Mechanical Wave (requires a medium)
 Longitudinal wave
 Caused by slight differences in air pressure
How do we get sound?
 Molecules vibrate at certain frequencies
 Speaker pushes
air in and out
All sounds are caused by vibrations
Tuning fork
Guitar String
Sound & Your Eardrum
Sound and your ear
Properties of Sound Waves
FREQUENCY  PITCH
 Measured in Hz
 Human hearing: 20 - 20,000 Hz
 Infrasonic (<20 Hz) Ultrasonic (>20,000 Hz)
Properties of Sound Waves
AMPLITUDE  INTENSITY
(How loud)
 Related to energy. . . higher amplitude, more energy
 Measured in db
 Measures how much the eardrum is displaced from rest
Decibels
A way of measuring intensity (how loud)
SOURCE
INTENSITY
LEVEL
# of times greater than
the Threshold of
Hearing (TOH)
Threshold of Hearing (TOH)
0 dB
1
Rustling Leaves
10 dB
10
Whisper
20 dB
100
Normal Conversation
60 dB
1,000,000
Busy Street Traffic
70 dB
10,000,000
Vacuum Cleaner
80 dB
100,000,000
Front Row of Rock Concert
110 dB
100,000,000,000
Threshold of Pain
130 dB
10,000,000,000,000
Military Jet Take-Off
140 dB
100,000,000,000,000
Instant Perforation of Eardrum
160 dB
10,000,000,000,000,000
 http://www.youtube.com/watch?v=xH8mT
2IQz7Y&safety_mode=true&persist_safety
_mode=1&safe=active
 But he uses transverse instead of
longitudinal
Web Quest
Stationary Source of Sound
 When the source is stationary, everyone
experiences the same frequency (same
pitch).
Moving Source of Sound
 When the source of the sound moves with
respect to the listener, the waves appear
stretched or compressed.
Doppler Effect
Take a listen
Doppler Effect
Use the Doppler apparatus and listen.
OPTIONAL
Sound Characteristics – Shock
Waves
 When a sound source or energy pulse
travels at the speed of sound, a
shockwave is produced.
 Source moving at speed of sound:
Real Life Shockwaves
Bullets often travel at or faster than the
speed of sound:
Mach 1
Shockwave
Real Life Shockwaves
Bullets often travel at or faster than the
speed of sound:
Real Life Shockwaves
So do jets and rockets!
Mach 1
Shockwave
Example
 Shockwaves
Sound Characteristics –
Resonance
 Sound waves resonate just like any other
wave. Feedback!
 Use the sound wave resonator apparatus
to measure the speed of sound!
Ben Underwood – The Boy who
sees without eyes
 Part 1
 Part 2
 Part 3
 Part 4
 Part 5