1. WHAT IS SOUND?

~ Nature of Sound ~ 1. What is sound? 2. Human Hearing 3. Properties of Sound 4. Interactions of Sound 5. Sound Quality

1. WHAT IS SOUND? A Sound wave is a LONGITUDINAL WAVE caused by vibrations of particles back and forth through a medium. Sound waves are mechanical waves and NEED A MEDIUM TO TRAVEL Sound waves travel in all directions from the source

2. Human Hearing

Human Hearing sound wave Outer Ear: vibrates ear drum Middle Ear: amplified by bones Inner Ear: converted to nerve impulses in cochlea

3. Properties of Sound

A. SPEED OF SOUND 344 m/s in air at 20°C 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

B. PITCH Pitch highness or lowness of a sound depends on frequency of sound wave High pitch=high frequency Low pitch=low frequency ultrasonic waves subsonic waves

DOPPLER EFFECT Have you ever noticed how the sound of a police car siren changes as it moves past you? The changes in pitch you hear are due to a phenomenon known as the Doppler effect. Look at the illustration of the police car to answer these questions. The police car has passed the woman standing on the sidewalk, but has not yet passed the man. Which observer hears the siren at a higher pitch—the woman or the man?

Doppler Effect moving toward you - pitch sounds higher change in wavelength due to the motion of the source. As the source moves, the waves become bunched up and the pitch (frequency) of the sound changes. moving toward you - pitch sounds higher moving away from you - pitch sounds lower

Doppler Effect http://www.fearofphysics.com/Sound/doppler.html http://www.colorado.edu/physics/2000/applets/doppler.html http://www.pbs.org/wgbh/nova/universe/moving.html

C. LOUDNESS Loudness volume of sound depends on energy (amplitude) of sound wave measured in decibels (dB)

Loudness measured in Decibels DECIBEL SCALE 120 110 100 80 70 40 18 10

4. INTERACTIONS OF SOUND Reflection Interference Resonance

A. REFLECTIONS OF SOUND WAVES Reflections of sound waves are called echos! Sound waves reflect best off smooth, hard surfaces ECHOLOCATION USE OF REFLECTED SOUND WAVES TO FIND OBJECTS

Ultrasonic waves are used to see with sound using reflection! Ultrasonic waves - above 20,000 Hz SONAR “Sound Navigation Ranging” Medical Imaging

B. Interference Interference When 2 or more waves overlap Constructive - louder Destructive - softer

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Sonic Boom Sounds from Moving Sources. A moving source of sound or a moving observer experiences an apparent shift of frequency called the Doppler Effect. If the source is moving as fast or faster than the speed of sound, the sound waves pile up into a shock wave called a sonic boom. A sonic boom sounds very much like the pressure wave from an explosion

C. Resonance = Forced Vibration when one vibrating object forces another object to vibrate at the same frequency results in a louder sound because a greater surface area is vibrating used in guitars, pianos, etc.

~ Music vs. Noise ` Music Noise specific pitches and sound quality regular pattern Noise no definite pitch no set pattern