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

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

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

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?

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)

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

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

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

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)

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

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