the nature of sound coach dave edinger physical science (8a)
TRANSCRIPT
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The Nature of SoundCoach Dave Edinger
Physical Science (8A)
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Objectives
• What is sound?
• What physical properties of a medium affect the speed at which sound travels through it?
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What is a Sound Wave?
• Sound waves carry energy through a medium without the particles of the medium traveling along.
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What is the medium through
which sound waves travel?
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What is a Sound?
• Sound is a disturbance that travels through a medium as a longitudinal wave.
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How are sound waves made?• Air is made up of tiny particles
• Vibrations generate a disturbance in the molecules in the air
• The force of the disturbance pushes the molecules closer together generating a compression
• In between vibrations, the molecules spread out and rarefactions are created.
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Sound Waves
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Sound Waves
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Sound Waves
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Pluck a guitar string………. • Plucking the string
causes vibrations
• The vibrations cause compressions and rarefactions
• The sound wave travels through the air in longitudinal wave form
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SING!• Vocal cords are like a guitar string
• When you speak, air is forced past your lungs and rushes past your voice box
• Larynx
• 2 folds of tissue vibrate creating sounds
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Let’s try it!
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How else can sound travel?• Sounds can travel
through solids and liquids
• Knock
• This causes vibrations in the medium
• The vibrations generate sound waves
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How far can the vibrations travel?• You can put your ear
on a train track and hear the train coming from miles away.
• Why?
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Limitations of Sound:• Sounds can
travel only if there is a medium through which to transmit the compressions and rarefactions
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Sound in Space• Sounds can not
travel through outer space
• No molecules in space to compress or rarefy
• There is no matter in space
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How does sound bend?• Sound waves bend out
(diffract) and spread when they hit a barrier or a hole in a barrier
•Diffraction – sound waves can bend and spread around a corner
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The speed of sound in different media:• The speed of sound depends on the
physical properties of the medium it travels through.
• Air at room temperature – 342 m/s
• The speed sound can travel through a medium depends on:– Elasticity– Density– Temperature
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Elasticity• Speed depends on how well the particles
in the medium bounce back after being disturbed
•Elasticity – the ability of a material to bounce back after being disturbed
• Examples:– Rubber band vs. clay– Solids are more elastic that liquids– Gases are not very elastic at all
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Density• The speed of sound depends on how
close together the particles of the substance are.
• Density – how much matter, or mass, there is in a given amount of space or volume
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Density Continued• Sound travels more slowly in denser
mediums
• More dense means more mass per volume
• The particles of a dense material do not move as quickly as those of a less dense material
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Temperature• Sound travels more slowly at
lower temperatures than at higher temperatures
• At low temperatures, the particles of a medium are sluggish
• Sound waves move and return to their original positions more slowly than they would at high temperatures.
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Objectives Review• What is sound?
• What physical properties of a medium affect the speed at which sound travels through it?