Unit 10 Lesson 2 Interactions of Sound Waves
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Unit 10 Lesson 2 Interactions of Sound Waves
Some Like It Hot
What affects the speed of sound?
• There are two main factors that affect the speed
of sound: the type of medium the sound travels
through, and the temperature of the medium.
• If we know these factors, we can predict the
speed of sound.
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Unit 10 Lesson 2 Interactions of Sound Waves
What affects the speed of sound?
• The speed of sound depends on the type of
matter, or medium, through which sound travels.
• The state of matter also affects sound waves.
• Sound travels fastest through solids, slower
through liquids, and slowest through gases.
• The more packed together the particles are, the
faster the wave will travel.
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Unit 10 Lesson 2 Interactions of Sound Waves
What affects the speed of sound?
• The speed of sound depends on the temperature
of a medium.
• Sound travels faster at higher temperatures than
at lower ones.
• Particles in a material move more quickly at
higher temperatures and transfer energy faster.
• Sound moves faster at higher temperatures and
slower at cooler temperatures.
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Unit 10 Lesson 2 Interactions of Sound Waves
Hello? Hello? Hello?
How do sound and matter interact?
• Sound waves do not travel easily through all
matter.
• Sound may bounce away from some surfaces.
Sound may be absorbed by other sources or
transmitted through a barrier
• Reflection is the bouncing back of a wave when it
hits a barrier. Sound waves reflect best off
smooth, hard surfaces.
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Unit 10 Lesson 2 Interactions of Sound Waves
How do sound and matter interact?
• Some matter absorbs sound waves better than
other matter.
• A rough wall will absorb sound better than a
smooth wall will.
• Soft materials, such as rugs and drapes, will
absorb sound better than hard surfaces will.
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Unit 10 Lesson 2 Interactions of Sound Waves
How do sound and matter interact?
• How will sound waves travel differently in each
room?
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Unit 10 Lesson 2 Interactions of Sound Waves
What is an echo?
• An echo is a reflected sound wave.
• The strength of the echo depends on the reflecting
surface.
• Echoes can be reduced using soft materials that
absorb the sound waves.
• Echoes can also be reduced using rough surfaces
that scatter the sound waves.
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Unit 10 Lesson 2 Interactions of Sound Waves
What is an echo?
• Some animals—such as dolphins, bats, and beluga
whales—use echoes to hunt for food and find
objects in their path.
• The use of reflected sound to find objects is called
echolocation.
• People use a type of echolocation called sonar
(sound navigation and ranging).
• Sonar is electronic echolocation used to locate
objects underwater.
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Unit 10 Lesson 2 Interactions of Sound Waves
What is an echo?
• How do bats use echolocation?
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Unit 10 Lesson 2 Interactions of Sound Waves
Boom!
How do sound waves interact with each
other?
• Interference happens when two or more waves
overlap and combine to form one wave.
• In music, beats happen when two sound waves
with nearly equal frequencies interfere.
• Since the frequencies are not quite equal, they
form a repeating pattern of constructive and
destructive interference that sounds loud and soft.
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Unit 10 Lesson 2 Interactions of Sound Waves
How do sound waves interact with each
other?
• When constructive interference occurs, waves
overlap and combine to form a wave with a larger
amplitude, or height.
• Constructive waves can cause very loud sounds,
such as sonic booms.
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Unit 10 Lesson 2 Interactions of Sound Waves
How do sound waves interact with each
other?
• In destructive interference, waves combine to
form a wave with a smaller amplitude.
• The sound will be softer because the amplitude is
decreased.
• Noise cancelling headphones use destructive
interference.
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Unit 10 Lesson 2 Interactions of Sound Waves
How does interference cause sonic
booms?
• Jet planes moving faster than the speed of sound
can produce a very loud sound called a sonic
boom.
• This sound can rattle and even break windows.
• When a jet travels very fast, it catches up to its
own sound.
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Unit 10 Lesson 2 Interactions of Sound Waves
How does interference cause sonic
booms?
• The waves pile up as a result of constructive
interference.
• This interference forms a high pressure area
called a sound barrier.
• If a jet travels fast enough, it breaks through the
barrier and forms a single shock wave that is
heard as a loud boom.
• The jet must travel at supersonic speeds, or
speeds faster than the speed of sound.
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Unit 10 Lesson 2 Interactions of Sound Waves
How does interference cause sonic
booms?
• How does this jet create a sonic boom?
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Unit 10 Lesson 2 Interactions of Sound Waves
Good Vibrations
What is resonance?
• Resonance happens when a sound wave matches
the natural frequency of an object and causes the
object to vibrate.
• If a sound wave in the room forces air in a
seashell to vibrate at its natural frequency,
resonance occurs.
• This resonance results in a big vibration that
sounds like the ocean when you hear it.
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Unit 10 Lesson 2 Interactions of Sound Waves
Where can resonance occur?
• All objects have a frequency, or set of frequencies,
at which they vibrate.
• These are called natural frequencies, or resonant
frequencies.
• Resonance will happen whenever an object
vibrating at or near the natural frequency of a
second object causes the second object to vibrate
as well.
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Unit 10 Lesson 2 Interactions of Sound Waves
Where can resonance occur?
• Resonance is important for making music.
• Vibrations make a sound that gets louder when it
forms a standing wave inside the instrument.
• A standing wave is a pattern of vibration that
looks like the wave is standing still.
• Resonance occurs when standing waves are
formed.
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Unit 10 Lesson 2 Interactions of Sound Waves
Where can resonance occur?
• Resonance can even occur in buildings, towers,
and bridges.
• Simple activities such as marching can create
resonance to cause a bridge to sway or collapse.
• Engineers plan their designs to prevent resonance
that could collapse a structure.
• Overlapping plates cause friction to keep
resonance from becoming destructive.
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