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Sound
• Sound is a longitudinal wave
•Sound, like all waves is generated by something
vibrating
•What is its medium?
Sound
• Without a medium, there is no sound
Sound
• Sound waves behave as all mechanical waves
do
• Human ears are capable of hearing 2020,000Hz roughly
• All sorts of things can create sound
How the Human Ear Works
Sound
• You lose your hearing as you
age, it’s called presbycusis,
what? I can’t hear you! Speak
up!
• You can also damage your ears
by being exposed to loud
sounds.
• Whenever you have “ringing” in
your ears, you have sustained
permanent hearing loss!
I Can’t Hear You
• Animals hear things differently than us!
How big is a sound wave?
• Sound travels at roughly 346 m/s (761 mph) in
air
• We can hear frequencies between 2020,000Hz (this is a generally accepted value)
• How long are the longest and shortest
wavelengths we can hear? Do the math!
• Longest 17.3 meters Shortest =1.7cm
Directional Hearing
• Humans can tell what way a sound came from
by the difference in time between when it
gets from one ear to the next
• We can’t tell if a sound is directly in front or
directly in back of us (with no reflection)
• We also can’t tell were a sound is coming from
if the wavelength is much longer than the
distance between our ears
• That’s why subwoofers don’t need to be
placed where the sound is coming from
Constructive and destructive
interference
• Interference applet
• When setting up a sound stage, engineers
have to worry about “dead spots” where the
sound is destructive interference is taking
place
Beats
• Beats-Periodic variation in the amplitude of a
wave that is due to the destructive
interference due to multiple sources with
slightly different frequencies.
• Beats applet (visual) in phase/out of phase
(under waves-> general -> beats)
• Second applet go to setup and then beats
Resonance
• Natural frequency-frequency at which
something naturally vibrates
• Resonance- The effect of when a vibrating
object forces another object with the same
natural frequency to vibrate
• Multi-pendulum
• Tacoma Narrow bridge
Real life
• So you say, Anderson, when am I going to use
this stuff in real life?
• Anderson says when you become a construction
worker!
Doppler Effect
• Doppler Effect- observed change in frequency
when there is relative motion between the
source of sound and the observer
• Applet 1
• Applet 2
• Doppler Rocket
Sound barrier
• When an object exceeds the speed of sound
for that medium, it creates a sonic boom
• The sonic boom happens anytime an object
goes faster than the speed of sound.
• Applet 1
• Youtube video
Decibel Scale
• Decibels (dB)- A measure of
the Intensity of a sound
wave, not necessarily the
perceived loudness.
• Decibel scale is an
exponential scale
• Each 10 decibels makes the
noise 10 times loud. For
example, a 80 dB sound it
1000 times as intense as a
50 dB sound
Rueben's Tube
• Youtube Video