Chapter 16.1 The Nature of Sound
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Transcript of Chapter 16.1 The Nature of Sound
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Chapter 16.1 The Nature of Sound
Pg. 540-545
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Question to think about…
• If a tree falls in a forest and no one hears it , does the tree make a sound?
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Sound Waves:
• Sound is a disturbance that travels through a medium as a longitudinal wave
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Making Sound Waves• A sound wave begins with a vibration• Sound waves are made up of compressions and
rarefactions • Example: – Striking a metal gong• When the gong is struck it vibrates• The vibrations disturb nearby air particles• Each time the gong moves to the right it pushes air
particles together creating a compression• Each time the gone moves to the left, the air particles
bounce back and spread out, creating a rarefaction
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How Sound Travels• Sound waves carry energy
through a medium without moving particles of the medium along
• Each particle of the medium vibrates as the disturbance passes.
• When the disturbance passes your ear you hear the sound
• A common medium for sound is air, but sound can travel through many other mediums
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Interactions of Sound
• Sound waves reflect off objects, diffract through narrow openings and around barriers, and interfere with each other
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Sound Waves and Reflection
• A reflected sound wave is called an echo
• The harder and smother the surface, the stronger the reflection– In rooms where there are soft
materials you don’t hear an echo because the soft materials absorb the sound
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Sound Waves and Diffraction
• Sound Waves do not always travel in a straight line
• Sound waves can also diffract, or bend, around corners
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Sound Waves and Interference
• Sound waves may meet and interact with each other
• When sound waves meet constructive or destructive interference can occur
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The Speed of Sound • All sound travels through the air at the same speed– At room temperature (20ᵒC) sound travels through the
air at 343 m/s
• The speed of sound is not always 343 m/s because sound waves travel at different speeds in different mediums
• The speed of sound depends on the characteristics of the medium that sound travels through – 1. Elasticity – 2. Density– 3. Temperature
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Speed of Sound: Elasticity • Elasticity is the ability of a material to bounce
back after being disrupted– The elasticity of a medium depends on how well
the medium’s particles bounce back after being disrupted
– In a more elastic medium the particles bounce back more quickly
– In a less elastic medium the particles bounce back slower
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Speed of Sound: Elasticity • The more elastic the medium, the faster sound
travels – Sound travels well in solids because they are
usually more elastic• Particles of solids do not move very far , so they bounce
back and forth very quickly as the compressions and rarefaction of the sound waves pass
– Most liquids are not very elastic and sound does not travel well
– Sound travels very slowly in gases because gases are not very elastic
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Speed of Sound: Density
• Density is how much matter, or mass, there is in a given amount of space, or volume.
• Sound travels more slowly in denser mediums– The particles of dense materials do not move as
quickly as those of less dense material.
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Speed of Sound: Temperature• Sound travels more slowly at lower
temperatures than at higher temperatures– This is because at low temperatures,
the particles of the medium move more slowly
– At low temperatures the particles are harder to move and return to their original positions more slowly. • Example: @ 20ᵒC 343 m/s @ 0ᵒC 330 m/s
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Speed of Sound: Temperature
• Since the temperatures are lower at higher altitudes, sound travels more slowly at higher altitudes