Chapter 15 Notes

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Chapter 15 Notes
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Section 15.1 - What are waves?

• Wave - a disturbance that transfers energy from
  place to place
• Medium - material through which a wave travels
  (solid, liquid, gas)
• Waves travel through the medium, but do not carry
  the medium itself with them.

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What are waves? (cont.)

• Duck overhead
• Waves crashing on beach do move medium due to
  shallow water
• Waves are created when a source of energy causes
  a medium to vibrate
• Vibration - repeated up-and-down or
  back-and-forth motion

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3 Types of Waves

• Transverse - waves that move the medium at right
  angles to the direction in which the waves are
  traveling. Example - long spring (label crest,
  trough and amplitude)
• Longitudinal (Compression) - waves that move the
  particles of the medium parallel to the direction
  in which the waves are traveling. Example -
  slinky
• Surface - Combinations of transverse and
  longitudinal waves. Example - waves on surface
  of the ocean

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Section 15.2 - Properties of Waves

• Amplitude - maximum distance the particles of the
  medium carrying the wave move away from their
  rest positions.
• Wavelength - The distance between two
  corresponding parts of a wave (crest to crest,
  trough to trough)

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Properties of Waves (cont.)

• Frequency - The number of complete waves that
  pass a given point in a certain amount of time.
  Measured in hertz (Hz)
• Speed - How far the wave travels in one unit of
  time
• Speed Wavelength ? Frequency
• Overheads - wave diagrams

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Section 15.3 - Interactions of Waves

• Reflection - When a wave hits a surface through
  which it cannot pass, it bounces back.
• Angle of incidence angle of reflection
  (diagram pg.482)
• Demo - bounce ball off wall

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Interactions of Waves (cont.)

• Refraction - When a wave moves from one medium
  into another medium at an angle, it changes speed
  as it enters the second medium, which causes it
  to bend.
• Example - shopping cart wheel in water, light in
  water in pool
• Diffraction - When a wave passes a barrier or
  moves through a hole in a barrier, it bends and
  spreads out
• Example - overhead

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Interactions of Waves (cont.)

• Constructive interference - two waves combine to
  make a wave with larger amplitude
• Destructive interference - two waves combine to
  make a wave with a smaller amplitude
• Example - use slinky for constructive and
  destructive interference

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Interactions of Waves (cont.)

• Standing wave - wave appears not to move
• nodes - locations of zero amplitude
• antinodes - locations of maximum amplitude
• Demo - spring
• Resonance - occurs when vibrations traveling
  through an object match the objects natural
  frequency
• Example - child on swing

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Section 15.4 - Seismic Waves

• When the stress in rock builds up enough, the
  rock breaks or changes shape, releasing energy in
  the form of waves or vibrations.
• Three types of seismic waves
• Primary waves - (P waves) longitudinal waves.
  Fastest seismic waves. Travel through all parts
  of the earth.
• Secondary waves - (S waves) transverse waves.
  Cannot travel through liquid (earths core)
• Surface waves - combination of longitudinal and
  transverse waves. Produce the most severe ground
  movements.

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Seismic Waves (cont.)

• Tsunami - huge surface waves on the ocean caused
  by underwater earthquakes.
• Seismograph - device that records the ground
  movements caused by seismic waves as they move
  through the earth