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The Nature of Sound
Section 3:
Interactions of Sound Waves
Essential Questions
How are echos made?
How can an echo help locate an object?
What is constructive interference?
What is destructive interference?
What is resonance?
Vocabulary
Echo – the bouncing back of a sound wave after striking a barrier
Echolocation – using reflected sound waves to find objects
Interference – combination of two or more waves into one wave• Can be constructive or destructive
Sonic boom – loud boom caused by an object traveling faster than the speed of sound
Vocabulary, continued
Standing wave – pattern of vibrations that look like a wave that is standing still
Resonance – when a vibrating object causes a second object to vibrate
Reflection of Sound Waves
Reflection – sound waves bouncing back after striking an object
• Also known as an echo
Echolocation – using echoes to find an object
• Used by some animals: dolphins, bats, some whales, some birds
Reflection of Sound Waves 2
Sonar (sound navigation and ranging) –electronic echolocation
• Sonar uses ultrasonic waves to find objects or create maps
Ultrasonography – using echoes to “see” inside a patient’s body
• Safer than x-rays
• Ex: commonly used to “look at” developing fetuses
Interference of Sound Waves
Interference – when two or more sound waves overlap
• Constructive interference – when waves overlap, the amplitude is increased so the sound becomes louder (Think: constructive = build)
• Destructive interference – waves begin to cancel each other out, decreasing the amplitude so the sound becomes softer (think: destructive = tear down)
Interference of Sound Waves 2 Supersonic speeds – faster than the
speed of sound
• The constructive interference creates a shock wave
Sonic boom – sound heard when a shock wave has occurred
• Can damage hearing and objects
Interference of Sound Waves 3
Standing wave – a wave that looks like it is standing still
• Maximum amplitude = constructive interference
• Seems to be still = destructive interference
Fundamental frequency – the one standing wave that you can see
Resonant frequency – frequency where standing waves can be seen
Resonance
Resonance – when a vibrating object causes a second object to vibrate
Used in musical instruments