What is Sound?Coke Bottle SongCoke Bottle- Mary Had a Little Lamb

Ch. 21 Notes

A. How are sound waves described?

1. Created by vibrations• Vibration= complete back and forth motion of an

object

2. 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

4. 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

B. How do humans detect sound?The Human Ear

1. Outer ear= funnel collecting sound waves; directs sound waves to eardrum to vibrate

2. Middle ear= 3 bones vibrate & increase vibrations and sends them to inner ear

3. Inner ear= cochlea fluid has waves that then transmit stimulus to nerves that send the signal to the brain

4. Animation- Anatomy of Ear

5. Video- How Old are Your Ears?

C. What are the properties of sound?

1. 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)

2. 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

3. 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

4. Amplitude – max. distance a sound wave is from rest position

• Louder sound = larger amplitude

5. Decibel (dB) (Video)• Unit expressing loudness

of sound• 120 dB= pain thresh hold

6. 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

D. How do sound waves interact?

1. Reflection= echo• Depends on surface (smooth, hard surfaces

works best)• Echolocation= the process of using sound

waves to find objectsEx: sonar

ultrasonography– type of echolocation used medically to “see” organs and unborn babies

Video- Reflection of Sound

Video- Echo and Reverb

2. 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)

3. 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

E. What is noise? Video- Noises We Hear

1. Most sounds are noise

2. Any undesired sound

3. Usually nonmusical

4. Random mix of pitches

5. Noise pollution– noise levels that cause pain and damage the human body

6. Music- Just Like an Echo Song