1. What is Sound? Coke Bottle Song Coke Bottle- Mary Had a Little Lamb
Ch. 21 Notes

2. How are sound waves described?
Created by vibrations
Vibration= complete back and forth motion of an object
Travels as longitudinal waves that consist of compressions( ) and rarefaction ( )
Longitudinal wave= motion of air molecules that are parallel to motion of the wave.
High pressure area
Low pressure area

3. Travels in all directions from source by vibrating air particles in place causing collisions that transmit energy, not matter
Requires a medium (therefore it can’t travel through a vacuum, and is a mechanical wave, too.)
Medium= matter/ substance through which a wave can travel; can be solid, liquid, or gas
FASTEST THROUGH SOLIDS!!
Video- Speed of Sound

4. How do humans detect sound?
The Human Ear
Outer ear= funnel collecting sound waves; directs sound waves to eardrum to vibrate
Middle ear= 3 bones vibrate & increase vibrations and sends them to inner ear
Inner ear= cochlea fluid has waves that then transmit stimulus to nerves that send the signal to the brain
Animation- Anatomy of Ear
Video- How Old are Your Ears?

5. What are the properties of sound?
Speed
Depends on medium
Faster in solids than in liquids than in gases (Why?? Table p.606)
Depends on temp. (cool T= slower sound wave)

6. Pitch (frequency)– how high or low a sound is perceived Determined by frequency
High frequency= high pitch
Low frequency= low pitch
Infrasonic– sounds lower than 20Hz
Ultrasonic– sounds higher than 20,000Hz
Human Ear – between 20Hz to 20,000Hz
Video- Frequency and Amplitude
Doppler Effect– the apparent change in frequency of a sound caused by the motion of the listener or sound source (Video- Doppler Effect)
Approaching sounds have higher pitch
Leaving sounds have lower pitch

7. Amplitude – max. distance a sound wave is from rest position
Louder sound = larger amplitude
Decibel (dB) (Video)
Unit expressing loudness of sound
120 dB= pain thresh hold
Oscilloscope - machine that converts sound waves into electrical signals that can be plotted on a graph, since sound waves are invisible
Allows sound wave's amplitude and frequency to be measured
Video- Sound Waves on the Oscilloscope

8. How do sound waves interact?
Reflection= echo
Depends on surface (smooth, hard surfaces works best)
Echolocation= the process of using sound waves to find objects
Ex: sonar
ultrasonography– type of echolocation used medically to “see” organs and unborn babies
Video- Reflection of Sound
Video- Echo and Reverb

9. Interference– the combining of sound waves constructively or destructively
Constructive: louder sounds, increased amplitude. Ex: bands, sound barrier, shockwave, sonic boom, etc.
Destructive: dead spots, softer sound, decreased amplitude
Standing waves– produced by interference (video)
Resonance– from object vibrating at or near a resonant frequency of a second object that causes it to vibrate, too.
(Sonic Boom- Occurs when sound waves that are in constructive interference forming a sound barrier are broken by an object traveling faster than the speed of sound. Sonic Boom Video)

10. 4. Refraction– sound waves being bent
Diffraction– bending of sound waves around barriers or through openings (Video- Diffraction of Sound Waves)
4. Refraction– sound waves being bent
Occurs b/c speed of sound
changes as medium properties
change (due to T or entering
different medium)
Video- Reflection and Refraction of Sound

11. What is noise? Video- Noises We Hear
Most sounds are noise
Any undesired sound
Usually nonmusical
Random mix of pitches
Noise pollution– noise levels that cause pain and damage the human body
Music- Just Like an Echo Song