Mav Mark 9/16/11

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Mav Mark9/16/11

• s 50 cm/s
• ? 10 cm
• f ?

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Characteristics of Waves

• Part II

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Reflection

• When an object or a wave hits a surface through
  which it cannot pass, it bounces back.
• Reflection is the bouncing back of a wave or
  object from a surface.
• For example, if you throw a ball at a wall, the
  ball bounces back. The ball is reflected by the
  wall.

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Reflection

• Sound waves bounce off walls and other hard
  surfaces. Reflected sound waves are called
  echoes.
• Light waves bounce off mirrors and other shiny
  surfaces. You see your face in a mirror because
  light from your face bounces from the mirror to
  your eyes.

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Reflection

• Law of Reflection - The angle of incidence is
  always equal to the angle of reflection.

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Refraction

• When a wave enters a new medium at an angle, one
  side of a wave changes speed before the other
  side, causing the wave to bend.
• Refraction is the bending of a wave due to a
  change in speed. Refraction happens only when a
  wave enters a new medium at an angle.

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Refraction

• Light travels slower through water than through
  air. So, when light enters water, it slows down.
• If a light wave passes from air into water - at
  an angle - one side of the light wave enters the
  water before the other side. This causes the
  light to bend.

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Diffraction

• When a wave moves around a barrier or through an
  opening in a barrier, it bends and spreads out.
• Diffraction is the bending and spreading out of
  waves. Diffraction happens when waves go around a
  barrier or through a hole in a barrier.

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Interference

• There are two types of interference constructive
  and destructive
• Interference is what happens between waves that
  bump into one another. When waves interfere, the
  waves combine to form a single wave.

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Interference

• Constructive interference happens when the crests
  of one wave pass through the crests of another
  wave. The two waves combine to make a wave with a
  larger amplitude.
• Destructive interference happens when the crests
  of one wave pass through the low points of
  another wave. The two waves combine to make a
  wave with a smaller amplitude.

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Types of Seismic Waves

• Seismic waves include P waves, S waves, and
  surface waves.
• Earthquakes cause waves that move through the
  ground. Earthquake waves are called seismic waves.

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Types of Seismic Waves

• P (primary) waves are longitudinal waves. P waves
  move more quickly than other types of seismic
  waves.
• S (secondary) waves are transverse waves. S waves
  cannot travel through liquids, including Earths
  liquid outer core. Because of this, if you are on
  the other side of the planet, you can primarily
  only feel P waves.
• Surface waves are a combination of of
  longitudinal and transverse waves. Surface waves
  move more slowly then P waves or S waves. They
  also cause more damage than P waves or S waves.

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Globe video
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Types of Seismic Waves

• Tsunamis are huge surface waves in oceans. They
  are caused by underwater earthquakes.

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Detecting Seismic Waves

• A seismograph records the ground movements caused
  by seismic waves are they move through Earth.
• Seismographs are instruments that measure
  earthquake waves.
• Seismographs can be used to find where an
  earthquake happened by measuring the time between
  a P wave and an S wave. Seismographs can also be
  used to find underground resources, such as oil
  and water.

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