3 I. 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 TRAVELSound waves travel in all directions from the source
10 B. PITCH Pitch highness or lowness of a sound depends on frequency of sound wavehuman range: ,000 Hzultrasonic wavessubsonic waves
11 C. LOUDNESS Loudness volume of sound depends on energy (amplitude) of sound wavemeasured in decibels (dB)
12 Loudness measured in Decibels DECIBEL SCALE1201101008070401810
13 D. DOPPLER EFFECTHave 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?
14 D.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 highermoving away from you - pitch sounds lower
17 IV. INTERACTIONS OF SOUND ReflectionInterferenceResonance
18 A. REFLECTIONS OF SOUND WAVES Reflections of sound waves are called echos!Sound waves reflect best off smooth, hard surfacesECHOLOCATIONUSE OF REFLECTED SOUND WAVES TO FIND OBJECTS
19 Ultrasonic waves are used to see with sound using reflection! Ultrasonic waves - above 20,000 HzSONAR“Sound Navigation Ranging”Medical Imaging
20 B. Interference Interference When 2 or more waves overlap Constructive - louderDestructive - softer
21 SONIC BOOMWhen a jet plane reaches the speed of sound, the sound waves in front of the jet combine by constructive interference. The result is a high density compression (high amplitude) compression called the sound barrier.
25 C. RESONANCE Forced Vibration when one vibrating object forces another object to vibrate at the same frequencyresults in a louder sound because a greater surface area is vibratingused in guitars, pianos, etc.
26 = Resonance = Resonance special case of forced vibration object is induced to vibrate at its natural frequency
27 The Tacoma Narrows Bridge Disaster = Resonance =“Galloping Gertie”The Tacoma Narrows Bridge DisasterWind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.
28 = Resonance =Beatsvariations in sound intensity produced by 2 slightly different frequenciesboth constructive and destructive interference occur
30 A. Music vs. Noise Music Noise specific pitches and sound quality regular patternNoiseno definite pitchno set pattern
31 Anechoic chamber - designed to eliminate reverberation. B. ACOUSTICAcousticsthe study of soundReverberationecho effect produced by the reflection of soundAnechoic chamber - designed to eliminate reverberation.