Waves & Sound The Nature of Sound  Speed of Sound  Human hearing  Doppler effect  Seeing with sound

Properties of Sound  Sound is produced from longitudinal waves created from vibrations  In air, sound waves spread out in all directions  Ruben’s TubeRuben’s Tube  Goop on Speaker Goop on Speaker

Speed of Sound  344 m/s (761mph) in air at 20°C (68°F)  Depends on:  Type of medium travels better through liquids and solids can’t travel through a vacuum  Temperature of medium travels faster at higher temps

Human Hearing  Intensity  volume of sound  depends on energy (amplitude) of sound wave  measured in decibels (dB)

Human Hearing DECIBEL SCALE

Human Hearing  Pitch  highness or lowness of a sound  depends on frequency of sound wave  human range: ,000 Hz ultrasonic waves subsonic waves

Human Hearing  When can you hear the scale?  Test Test

Human Hearing  Sound waves are funneled through the fleshy part of your ear down the ear canal  The ear canal ends at the ear drum (thin flat piece of tissue)  The sound waves hit the ear drum causing it to vibrate  The vibrations travel through 3 tiny bones (hammer, anvil and stirrup)

Human Hearing  When vibrations hit the stirrup, waves are sent through the snail shaped cochlea  The cochlea contains a flexible membrane called the basilar membrane  The basilar membrane then vibrates hair cells that stimulate nerve fibers that send impulses to the brain  The brain interprets these impulses as sound!

Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea

Doppler Effect  Doppler Effect  change in wave frequency caused by a moving wave source  moving toward you - pitch sounds higher  moving away from you - pitch sounds lower  Simulation Simulation

Doppler Effect Stationary sourceMoving sourceSupersonic source same frequency in all directions waves combine to produce a shock wave called a sonic boom higher frequency lower frequency

Sonar  A sonar system determines distance by measuring the time it takes for sound waves to be reflected back to a surface  Knowing the speed of sound in the medium, d=rt can be used  Ultrasonic waves are used (about 20,000 Hz)  These waves are easily controlled

Ultrasound Imaging  Ultrasonic waves can be used to produce sonograms too! Medical Imaging SONAR “Sound Navigation Ranging”