Waves!!

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Waves!!

• April 14, 2010

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Waves start with a VIBRATION

• Something moving back and forth
• Periodically
• Like a pendulum
• Or a spring

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Waves A traveling disturbance
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Why waves?

• Imagine a buoy on the ocean
• What happens to it as waves go by?

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Why waves?

• Waves carry energy from place to place
• The stuff stays put
• The energy is transmitted through the wave!

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Wave Properties

• Crest Top of Wave
• Trough Bottom of Wave

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Wave Properties contd

• ? Wavelength (crest to crest)
• H Wave Height (crest to trough)
• A Amplitude (mid-line to crest or trough-1/2 of
  wave height)

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Wave Frequency

• Number of times a wave passes a specific point in
  a given amount of time.
• Or cycles per second
• Frequency Wave Speed
• Wavelength
• Units Hertz (waves per second)

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More definitions

• Period ?
• The time it takes to complete one full cycle.
• Frequency ?
• The number of cycles per second.
• Velocity frequency x wavelength
• V ?f

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Speed

• Measured in meters per second.
• v wave length x frequency
• Or
• V ? f

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Frequency and wave length deal with

• Light color
• Sound pitch

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Electromagnetic Spectrum
Energy that is emitted by accelerating electric
charges. Energy travels in waves.
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(No Transcript)
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Amplitude and wave height deal with

• Light brightness
• Sound loudness

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Transverse waves

• The vibration is at right angles to the direction
  the wave is traveling.

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Longitudinal Waves

• The vibration is ALONG the direction the wave is
  traveling.

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Hooked on Labs!

• Hookes Law F ks
• Does the period of a wave depend on the strength
  of the spring?

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Waves Day 2

• April 19, 2010

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Lab T of springs

• What affected the period?
• T 2p(m/k)½
• How close does your data fit?

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Review

• What type of wave is this?

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Review

• And this one?

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Review some more

• Frequency ?
• number of times a wave passes a specific point in
  a given amount of time.
• Wave Length ?
• distance from crest to crest.
• Amplitude ?
• distance from mid-point to crest

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What I didnt tell you

• The speed of a wave through a medium is constant.
• Take sound traveling in air for example

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New for today

• Interference patterns
• Wave reflection
• Standing waves
• Doppler

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Interference

• What happens when waves overlap or touch

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Interference

• Can be Constructive
• crest lines up with another resulting in adding
  effect
• More or less energy?
• The USCGC Ironwood

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Interference

• Or can be Destructive
• Crest overlaps a trough resulting in reducing
  effect.
• smaller amplitude

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(No Transcript)
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Wave reflection

• What happens when a wave hits an obstruction?
• Case 1 Rope tied around post free to move up
  and down
• Case 2 Rope tied to a post
• Think about it and convince your neighbor

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Standing waves

• They are the result of interference
• Often due to incident wave (original) coming in
  contact with reflected wave
• Ocean surf
• Or Hood River

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To move or not to move

• Nodes
• Dont move!
• Anti-nodes
• Move the most!!

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Lab

• Read the instructions
• Be careful with the slinkies!

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Waves Doppler Sound

• April 21, 2010

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Last time

• Interference 2 types!
• What are they called?
• What happens for each one?
• If sound travels at 340 m/s in air
• Does it matter if the sound has a high pitch
• or a low pitch?

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Slinky Lab

• Did the wave speed change when it had a bigger
  amplitude?
• Did the wave speed change when you pulled it
  tighter?
• What happened when waves met mid-slinky?
• What did you have to do to increase the of
  nodes?

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Today

• Notes on Doppler
• Focus on sound
• Lab exploring wave speed and reflection

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Doppler Effect

• Ever heard of the Doppler Effect?

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Doppler Effect explain to a friend
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Doppler

• If the wavelength gets smaller
• The frequency must get bigger
• Remember
• Velocity wavelength x frequency

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Sound waves

• What is sound?
• Mechanical wave requires a medium
• Think ping pong balls
• Move out in a 3-D sphere
• Compression wave
• Compresses air molecules together
• And then they bounce back

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Speed of sound

• Sound travels at a constant speed through air
  340 m/s (about 760 mph)
• More or less
• We can change this
• If we increase the temperature
• If we add humidity

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Sound waves

• We hear certain frequencies
• 20 20,000 Hz
• Different animalsdifferent frequencies
• Dogs hear _____(?) pitch
• Elephants what do you think?
• Frogs use pitch to decipher mating calls

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Sound wave properties

• Amplitude
• How loud the sound is
• Frequency and wavelength
• The pitch (how high or low the note is)
• Generally speaking
• Speed is greater through solids than liquids
• And liquids faster than in air

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The Sound Barrier

• Doppler effect
• But if you travel as fast as the wave is moving

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Speed of Sound

• Flying at the speed of sound (330 m/sec) you
  build up a series of pressure waves.

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Finally breaking the barrier

• Once it gets past this barrier the ride smoothes
  out
• No longer fighting the pressure waves.

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Bow Wave

• When an object outruns the waves it produces, a
  wave is created at the edges in a V shape

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Sonic Cone?

• Sound is a 3-D wave
• Invisible cone of sound that stretches out toward
  the ground.
• Shock wave causes a sonic boom

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Sonic boom is continuous
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To increase the intensity of a sonic boom

• Increase the size of the airplane.
• Displaces more air - stronger shock waves
• Lower the altitude of the plane
• Shock waves have less distance to travel before
  hitting the ground

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Other sonic booms

• Bullets
• Bullwhips
• Towel snap
• Note these objects do not produce a sound, but
  when the sound barrier is broken they produce
  their own sound.

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Huygens Principle
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Lab

• Lets read the instructions
• Be responsible with the water

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Waves and Sound

• April 23, 2010

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Todays Plan

• Homework - review
• Continued Sound notes
• music, resonance, etc.
• Another wave lab

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Sound wave properties

• Amplitude
• How loud the sound is
• Related to its energy
• Frequency and wavelength
• The pitch (how high or low the note is)
• Generally speaking
• Speed is greater through solids than liquids
• And liquids faster than in air

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Sound waves

• Sound waves are compression waves
• Longitudinal waves
• Move out in a 3-D sphere
• We hear certain frequencies
• 20 20,000 Hz
• Different animalsdifferent frequencies
• Dogs, elephants, frogs

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Huygens?

• Visit Huygens Principle
• http//frank.harvard.edu/paulh/misc/pics/huygens_
  96.mp3

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Huygens Principle

• Each point on a wave front is the center of a
  circle
• What happens when you hit a partial boundary?

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Sound speed

• v f?
• The frequency of middle C is 264 Hz
• Sound travels at 343 m/s
• What is the wavelength?

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Double the frequency and you go up an octave.

• 440 Hz to 880 Hz octave

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Resonance

• All things have a natural vibration frequency
• When an object vibrates
• It tends to cause other items to vibrate
• Same natural frequency?
• Resonance occurs

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Ever watch the blinkers?

• And yours is out of sync with the guy in front of
  you?
• Or your windshield wipers are just out of sync
  with the music your listening to?
• Every once in awhile they match up!
• Right?

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Beats

• When the frequencies are just a bit off
• You hear pulses or beats
• Systematic wave interference
• Constructive and
• Destructive

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of Beats

• How can you determine the number of beats (per
  second)?
• Subtract the frequencies
• We can generally only distinguish about 10 beats
  after that we just hear a different pitch

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Forced vibrations and natural frequency

• All objects have a natural frequency the sound
  they make when its material is sent in motion.
• Forced vibration are when we use an object to
  make a second object to vibrate at a certain
  frequency.

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Resonance

• Frequency of a forced vibration on an object
  matches the natural frequency.
• Result dramatic increase in amplitude for the
  second object!

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How do we hear?

• The pinna, the outer part of the ear, serves to
  "catch" the sound waves.
• The eustachian tube allows the air pressure on
  both sides of the eardrum remains equal and lets
  your eardrum move freely back and forth
• The eardrum is rigid, and very sensitive. Even
  the slightest air-pressure fluctuations will move
  it back and forth.

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How do we hear?

• Cochlea in the inner ear conducts sound through a
  fluid, instead of through air. The small force
  felt at the eardrum must be amplified by the
  middle ear.

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Cochlea

• It's made of 20,000 to 30,000 reed-like fibers
  that extend across the width of the cochlea.
• The fibers are different lengths
• This gives the fibers different resonant
  frequencies.

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Organ of Corti

• Contains thousands of tiny hair cells. It extends
  across the length of the cochlea.
• When the wave finally reaches the resonant
  point...
• They send an electrical impulse through the
  cochlear nerve.

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To the Beach!

• Exploring waves

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Harmonics!

• April 27, 2010

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Today

• Sand waves http//www.lps.ens.fr/douady/SongofDun
  es/MovieCailleron.html
• Notes on Harmonics
• Review Sheet
• Lab Resonance

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Beats me

• Compare the sound with a known frequency
• No beats?
• They are at the same frequency.

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Forced vibrations and natural frequency

• All objects have a natural frequency the sound
  they make when its material is sent in motion.
• Forced vibration are when we use an object to
  make a second object to vibrate at a certain
  frequency.

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Resonance

• Frequency of a forced vibration on an object
  matches the natural frequency.
• Result dramatic increase in amplitude for the
  second object!

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Music sound that is organized by people.White
noise sounds that are a mixture of all
different wave lengths.
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Standing waves In reality, only waves that
survive long enough to hear are those the right
length to produce standing waves.
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Harmonics

• Natural frequencies harmonics of the
  instrument.
• Forced into vibrating at one of its harmonics by
  resonance

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Brass instruments

• Vibrate the mouth piece
• It works when frequency matches natural
  frequency of air in tube

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Wind Instrument same principle, but the reeds
vibrate as wind moves over them, causing a
variety of frequencies.
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String Instrument string movement causes
different frequency.
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Voice vocal cords vibrate, air in nasal passage
and mouth resonates.
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I guess start with waves

• What are they?

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Review

• April 29, 2010

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Wave Parts
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Wave Types

• L and T
• M and E

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Wave characteristics

• Energy travels not the particles
• Speed of sound through different mediums?
• Effects of density
• Generally
• The denser the medium, the faster the wave
• No easy answers on this one

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Wave equations

• Frequency speed / wave length
• Period 1 / frequency
• Frequency 1 / period

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Sound wave characteristics

• Pitch
• Loudness

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Interference

• Constructive
• Destructive

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Standing waves

• Nodes
• Antinodes

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Doppler Effect

• What does it look like?

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Doppler Effect in Universe

• Red vs. Blue shift (low freq vs. high freq)

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Bow Waves and Shock Waves

• Can you use the Doppler effect to draw and
  explain these?

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Sound type of wave?
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Transmitting sound

• Is sound faster in water or air?
• Metal or water?
• Soil or helium?
• Why?

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Resonance examples?

• What is your natural frequency?
• Can an object be forced to vibrate?

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Beats

• How are they determined?
• What are they?

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4 tuning forks live in the woods...

• Fork A 2 hertz
• Fork B 4 hertz
• Fork C 2 hertz
• Fork D 6 hertz

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Huygens principle
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Huygens Principle Every point on a wave is a
source of new circular waves.
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This principle can be used to explain the bending
of waves around a barrier or through a hole.
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Huygens principle on different size openings