The Energy of Waves

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The Energy of Waves

• Physical Science

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Section 1 The Nature of Waves

• A wave is any disturbance that transmits energy
  through matter or space.
• Examples
• ocean waves, microwaves, sun waves, and sound
  waves (radio, telephone and voice)

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Waves and Energy

• Waves move through a medium, which is the
  substance through which a wave can travel.
  Example sound travels through air (air is the
  medium).
• The waves travel through the medium, but the
  medium does not travel with the waves. For
  example water waves. It looks like the water
  is moving forward, but it is only moving up and
  down with the waves.

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Waves Transfer Through a Medium

• When the energy of a wave transfers through a
  medium, the particles in the medium vibrate, and
  it passes the energy to the next particle, which
  also vibrates.
• Example sound through the air. When you
  release the energy into the air, it causes the
  air particles to vibrate. That is how sound
  travels.
• Question When would you scream but not be heard?

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Energy Transfer Without a Medium

• Electromagnetic waves are waves that dont
  require a medium, so they can travel through a
  vacuum. These waves include visible light,
  microwaves, TV/radio signals, and Xrays.
• They can travel through a medium, but they dont
  need one.

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Light Years

• Because planets and stars can be very, very far
  away, they are measured in light years, the
  amount of time it takes light to travel. Since
  light travels at 299,792,458 meter per second,
  how could you find out how many meters it travels
  in a year?
• This means, when you see stars at night, the
  light you are seeing could have been emitted by
  the star before the Earth was even formed!

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Types of Waves

• 3 types transverse, longitudinal and surface
  waves
• Transverse Waves Waves in which the particles
  vibrate with an up-and-down motion. The
  particles in a transverse wave move across
  (perpendicular) the direction the wave is
  traveling. The top of each wave is called a
  crest, and the bottom of each wave is called the
  trough. Example all electromagnetic waves.

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Transverse Waves
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Longitudinal Waves

• In a longitudinal wave, the particles of the
  medium vibrate back and forth along the path that
  the wave travels.
• Think of the coils on a spring. You can stretch
  out the coils (rarefaction) and then let them
  bounce back (compression). In a longitudinal
  wave, the compressions are the crests of the
  wave, and the rarefactions are the troughs.
• Example sound waves

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Longitudinal Waves
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Surface Waves

• A combination of longitudinal and transverse
  waves is called surface waves. They look like
  transverse waves, but the medium moves in circles
  instead of up and down.
• Ocean waves are surface waves because they travel
  at the waters surface, where the water meets the
  air.

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Surface Waves
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Section 2 Properties of Waves

• Have you ever been on a boat on the water that
  wasnt moving? Do you remember the gentle
  rolling of the boat on the waves?
• Did you ever have a speeding boat pass by? If
  so, what did your boat do?
• There are 4 properties of waves amplitude,
  wavelength, frequency, and wave speed.

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Amplitude

• The property of waves that is related to the
  height of the wave is called amplitude. The
  amplitude of a wave is the maximum distance the
  wave vibrates from its rest position. The larger
  the amplitude, the taller the wave.
• It takes more energy to move a larger wave, so a
  wave with a large amplitude carries more energy
  than a wave with a small amplitude.

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Ocean Waves vs. Tsunami
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Wavelength

• A wavelength is the distance between any two
  adjacent crests or compressions, or the distance
  between any two adjacent troughs or rarefactions.

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The Power of Waves

• http//www.abc.net.au/news/specials/japan-quake-20
  11/

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Wavelengths
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Frequency

• Frequency is the number of waves (either the
  crest or the trough) that pass a given point in a
  given amount of time.
• You can measure frequency by counting the number
  of troughs or crests (one or the other, not both)
  during that time. It is measured in hertz (Hz).
  
• A hertz is equal to one wave per second. The
  higher the frequency, the more energy the wave is
  carrying.

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Wavelength and Frequency

• Because wavelength and frequency are closely
  related, you can see how the amount of energy the
  wave is carrying affects both.
• The more energy a wave has, the shorter the
  wavelength, the greater the frequency.
• The less energy a wave has, the longer the
  wavelength, the less frequency.

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Dont Touch that Dial!

• Think about your favorite radio station what is
  it?
• The number is the frequency of the waves that
  station is emitting.
• Which have higher frequencies, AM or FM stations?

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Wave Speed

• Wave speed is the velocity at which a wave
  travels. You can calculate it as
• Velocity frequency x wavelength or
• V f x ?
• To calculate wave speed, you would take the
  distance (between crests or troughs), and divide
  it by the time it takes to get a certain point.

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Wilberts Dilemma
The water waves below are traveling along the
surface of the ocean at a speed of 2.5 m/s and
splashing periodically against Wilbert's perch.
Each adjacent crest is 5 meters apart. The crests
splash Wilbert's feet upon reaching his perch.
How much time passes between each successive
drenching? Answer and explain using complete
sentences.
The water waves below are traveling along the
surface of the ocean at a speed of 2.5 m/s and
splashing periodically against Wilbert's perch.
Each adjacent crest is 5 meters apart. The crests
splash Wilbert's feet upon reaching his perch.
How much time passes between each successive
drenching?
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Wilberts Dilemma

• How to solve Wilberts problem
• If Velocity frequency x wavelength then
• 2.5m/s ? X 5 m
• frequency .5

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Section 3 Wave Interactions

• Planets do not emit light. So why does the moon
  shine so brightly, particularly a full moon?
• Reflection occurs when a wave bounces back after
  striking a barrier. All waves can be reflected.
  
• What do you call reflected sound waves?

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Wave Interactions

• Refraction is the bending of a wave as it passes
  at an angle from one medium to another.
• Have you ever looked down at your feet when you
  are standing in a pool? What have you noticed
  about your feet and legs?

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Mutant Student?

• When waves move to a different medium, they begin
  traveling at a different speed. The reason why
  your legs look like the are in the wrong place
  is because the light waves that traveled through
  the air go through the water at a different
  speed. As soon as the wave hits the water, it
  bends as it slows down, so your eyes see your
  legs further out than they really are!

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Diffraction

• Most waves travel in a straight line (such as
  light waves). However, some waves can curve or
  bend when they reach the edge of an object. This
  bending is called diffraction.
• Sound waves can diffract because they have longer
  wavelengths than light and can bend around the
  corners.

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Reflection, Refraction and Diffraction

•  
• http//www.youtube.com/watch?vSmoo3jKtsDI
• http//www.acoustics.salford.ac.uk/schools/teacher
  /lesson3/flash/whiteboardcomplete.swf

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Interference

• Have you ever walked into a large party or crowd,
  and you hear a lot of people talking. You cant
  understand anyone because too many people are
  talking. This is an example of interference.
• Interference is when 2 or more waves share the
  same space, so they overlap.

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2 Types of Interference

• Constructive Interference When the crest of one
  wave overlaps the crest of another wave. This
  increases the energy of the wave, so it has a
  higher amplitude. Example a band playing
  instead of just 1 person.
• Destructive Interference when the crest of one
  wave matches the trough of another wave. They
  cancel each other out, so all you get is noise.
  This is what happens in a crowd.

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Constructive and Destructive Waves
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Standing Waves

• A standing wave is a wave that forms a stationary
  pattern in which portions of the wave are at the
  rest position (destructive), while other portions
  have a large amplitude (constructive). It
  happens as the wave is traveling back and forth
  it looks like it is standing still, but energy is
  traveling through the medium.

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Resonance

• Standing waves cause resonance frequencies. In
  other words, the medium vibrates with the same
  frequencies as the wave.
• For example, when you strike an object, it begins
  to resonant with the same frequency of the energy
  that you struck it. Example a drum. The
  sound you hear is the vibration of the wave in
  the air that matches the vibration of the energy
  that you used to hit the drum.

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Resonance Videos

• https//www.youtube.com/watch?vJDnNmLkQ3Bc
• www.youtube.com/watch?vofESdVdX-fY

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Tacoma Narrows Bridge

• In 1940 a suspension bridge was built in Tacoma,
  Washington.
• Suspension bridges are designed to sway in the
  wind to a certain degree, which gives them their
  own energy waves.
• The high winds on Nov. 7th, 1940 matched those
  waves of the bridge (constructive waves), which
  amplified the bridges movement, causing its
  collapse.

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Tocoma Narrows Bridge Collapse

• https//www.youtube.com/watch?vnFzu6CNtqec

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The New Tacoma Narrows Bridge