Waves

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Waves

• Unit 4 Pages 334 to 421
• Chapter 8 in text

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What do you already know?

• What is a wave? (where can you find this
  info???
• Where do we see waves in our everyday lives?
• Do we see all waves?
• Why are waves important to physicists?

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With the person next to you

• Create a list of as many waves you can think of
  in your everyday lives
• 1 minute! Go!

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Waves - Everyday

• Earthquakes
• Tsunamis
• Sound waves
• Radio waves
• Light waves
• Regular ocean waves
• Springs (Slinky!)
• car suspension

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NOTE

• Light may or may not behave as a wave. There are
  two theories but light as a wave is the main
  theory some physicists believe light behaves as
  a wave of electromagnetic radiation
• Other theory Some physicists believe light is
  made of massless particles called photons not
  waves.
• Most physicists believe that light behaves as
  both physics 12!!!

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What is a wave (in physics)?

• Wave a disturbance that transfers energy
• Whether ocean waves, waves on a string,
  earthquake waves, or sound waves in air, they all
  have a vibration as their source.
• Waves move large distances across the surface of
  a lake or the sea, yet the water itself does not
  travel those distances. Only the ENERGY!

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Why are waves important to physicists?

• http//www.youtube.com/watch?vTGaM8pdnr50feature
  related
• http//www.youtube.com/watch?featureSeriesPlayLis
  tvXoYBAsHHXsklistPLFF513AD10F64B864
• http//www.bing.com/videos/search?qsinusoidalwav
  e2cclassroomdemowithmusicFORMHDRSC3viewde
  tailmidCE19F9685E15A9EC09A9CE19F9685E15A9EC09A9
• Waves are very important in engineering
  (buildings, bridges), seismology, etc. Waves
  explain how ENERGY MOVES.

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Other Words for Wave

• Vibration
• Wiggle
• Oscillate

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What do you need to cause a vibration?

• FORCE!

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Summary Slide

• Wave a disturbance that transfers energy
• Waves explain how ENERGY MOVES.
• Only the energy of a wave moves not the
  material itself
• Waves are used in seismology, engineering, sound
  technology, light technology, radiation, solar
  energy, etc.

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Summary Slide

• A wave needs a force to start and end.
• Waves are also called vibrations and oscillations.

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You were asked for homework to define the
following

• Mechanical waves
• Electromagnetic waves
• Transverse waves
• Longitudinal waves
• Surface waves
• Give an example of each type of wave.

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Mechanical Waves

• A mechanical wave is a wave that requires a
  medium in order to transport energy from one
  location to another.
• Example Sound waves

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Question

• If waves need a medium, how does sound energy get
  transferred through the air?

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Electromagnetic Waves

• An electromagnetic wave is a wave that is capable
  of transmitting its energy through a vacuum
  (i.e., empty space).
• Electromagnetic waves are produced by the
  vibration of charged particles.
• Example Light waves
• Light travels through space (no medium) from the
  sun to Earth

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Types of Waves

• There are three types of mechanical waves.
• 1. Transverse
• 2. Longitudinal
• 3. Surface

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Transverse Waves
Transverse waves are when the displacement is
perpendicular to the direction of the wave
Transverse waves are the ones most people can
draw. Example. S waves (earthquakes),
radiowaves, x-rays, and light waves (all
electromagnetic waves)
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• All electromagnetic waves are transverse waves.
• http//www.youtube.com/watch?vUHcse1jJAto

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Longitudinal Waves
Longitudinal waves are when the displacement is
parallel to the direction of the wave
Longitudinal waves travel through liquid
(tsunamis) Example P waves (geology), Sound
waves, ultrasound waves
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• http//www.youtube.com/watch?vRbuhdo0AZDU
• http//www.gcse.com/waves/waves2.htm

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Surface Waves

• A surface wave is a wave in which particles of
  the medium undergo a circular motion. They are
  typically in fluids (water or gas).
• Example Water ripples on the surface of the pond

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Questions for you!

• 1. A transverse wave is transporting energy from
  east to west. The particles of the medium will
  move_____.
• east to west only
• both eastward and westward
• c. north to south only
• d. both northward and southward

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• Answer D
• The particles would be moving back and forth in a
  direction perpendicular to energy transport. The
  waves are moving westward, so the particles move
  northward and southward.

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• 2. A wave is transporting energy from left to
  right. The particles of the medium are moving
  back and forth in a leftward and rightward
  direction. This type of wave is known as a ____.
• A. Longitudinal
• B. Transverse

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• LONGITUDINAL!

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In groups

• 1) Create a transverse wave with a slinky.
• 2) Create a longitudinal wave with a slinky.
• 3) Create an organizational chart/diagram/Venn
  diagram to show the types of waves and an example
  of each.

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• Make a longitudinal wave with a slinky
• You produce a different wave when you move your
  hand backwards and forwards along the slinky.
  This sort of wave is a longitudinal wave. The
  particles carrying the wave in the slinky move
  backwards and forwards along the direction of
  wave motion.

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• Make a Transverse Wave using the slinky
• When using a slinky, move your hand from side to
  side some humps move away from you along the
  slinky. Although the waves move along the
  slinky, the movement of the slinky is side to
  side. This is a transverse wave. The particles
  carrying the wave in the slinky move at right
  angles to the direction of wave motion.

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Bobbleheads

• In groups
• http//www.physicsclassroom.com/class/waves/u10l0a
  .cfm
• How does a bobblehead act like a wave or a
  vibration?
• How does the vibration start?
• Why does the vibration end?

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Tuning Fork

• How does a tuning fork act like a wave or a
  vibration?
• How does the vibration start?
• Why does the vibration end?

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Question

• Minute after minute, hour after hour, day after
  day, ocean waves continue to splash onto the
  shore. Explain why the beach is not completely
  submerged and why the middle of the ocean has not
  yet been depleted of its water supply.

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Answer

• Ocean waves do not transport water. An ocean wave
  could not bring a single drop of water from the
  middle of the ocean to shore. Ocean waves can
  only bring energy to the shore the particles of
  the medium (water) simply oscillate about their
  fixed position. As such, water does not pile up
  on the beach.

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• TRUE or FALSE
• In order for John to hear Jill, air molecules
  must move from the lips of Jill to the ears of
  John.

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FALSE!

• A sound wave involves the movement of energy from
  one location to another, not the movement of
  material. The air molecules are the particles of
  the medium, and they are only temporarily
  displaced, always returning to their original
  position.

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• 3. Describe how the fans in a stadium must move
  in order to produce a longitudinal stadium wave.
  How would they make a transverse wave?

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• The fans will need to sway side to side. Thus, as
  the wave travels around the stadium they would be
  moving parallel to its direction of motion. If
  they rise up and sit down, then they would be
  creating a transverse wave.

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• 4. A science fiction film depicts inhabitants of
  one spaceship (in outer space) hearing the sound
  of a nearby spaceship as it zooms past at high
  speeds. Critique the physics of this film.

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• This is an example of faulty physics in film.
  Sound is a mechanical wave and could never be
  transmitted through the vacuum of outer space (no
  medium!)

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Quick Review

• 1) What 2 things do ALL waves need?
• 2) What do mechanical waves need that
  electromagnetic waves dont need?
• 3) What are the three sub-types of mechanical
  waves? Give an example of each.
• 4) Which of these sub-types is always an
  electromagnetic wave? Give an example of an
  electromagnetic wave.

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Answers

• 1) Pulse/disturbance/force to start the wave and
  Energy
• 2) Mechanical waves need a medium to carry the
  energy from one point to another
• 3) Transverse (light), Longitudinal (sound),
  Surface (pebble dropped in a pond)
• 4) Transverse (light, xrays)