Waves and Tides (PowerPoint)

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					Waves and Tides
Chapter 16, Section 2

• Ocean waves are energy traveling along
  the boundary between ocean and
• Waves transfer energy through the ocean,
  that’s why even on a calm day in the
  middle of the ocean there may still be
  waves from a far off storm
Wave Characteristics
• Most ocean waves obtain their energy and
  motion from the wind
• Crests – the tops of the waves
• Troughs – the bottoms of the waves
• Wave Height – the vertical displacement
  between crest and trough
• Wavelength – the horizontal distance
  between two successive crests or two
  successive troughs
• Wave Period – the time it takes one
  wavelength to pass a fixed position
Wave Characteristics

• The height, length, and period that are
  eventually achieved by a wave depend on
  three factors: (1) wind speed; (2) length
  of time the wind has blown; and (3) fetch
• Fetch – distance that the wind has
  traveled across open water
Wave Motion
• Waves can travel great distances across ocean
•   As a wave travels, the water particles pass the
    energy along by moving in a circle; so the water
    doesn’t move, only the energy
•   Circular orbital motion allows energy to move
    forward through the water while the individual
    water particles that transmit the wave move
    around in a circle
•   The wind energy is not only transmitted along
    the surface, but also downward
Anatomy of a Wave
Breaking Waves
• As long as a wave is in deep water, it is
    unaffected by water depth
•   When a wave approaches shore, the water
    becomes shallower and influences wave
•   As a wave advances on the shore, the slightly
    faster waves further out will catch-up and
    decrease the wavelength, making the wave
    grow steadily higher
•   When a critical point is reached, the wave is too
    steep to support itself and the wave front
    collapses, or breaks, and the water advances up
    the shore
Breaking Waves
• Tides are regular changes in the elevation of the
    ocean surface
•   Other than waves, they are the easiest ocean
    movements to observe
•   Newton showed that there is a mutually
    attractive force between any two bodies, Earth
    and the moon
•   Ocean tides result from differences in the
    gravitational attraction exerted upon different
    parts of Earth’s surface by the moon and, to a
    lesser extent, by the sun
The Cause of Tides
• The primary body that influences the tides is the
•   The gravitational pull is greatest on the side of
    Earth closest to the moon, causing Earth to be
    stretched slightly
•   On the side of Earth closest to the moon, the
    pull of the moon’s gravity on the oceans is
    greater than it is on solid Earth
•   Water will flow towards this tidal “bulge”,
    creating a high tide
•   As Earth rotates, it will go “through” the tidal
    bulges, resulting in alternating high and low
Cause of Tides
Tidal Cycle
• The sun also produces tidal bulges, slightly
    smaller than those produced by the moon
•   The influence is most noticeable during new and
    full moon phases (Earth-moon-sun are aligned),
    causing larger tidal bulges
•   Tidal Range – the difference in height between
    successive high and low tides
•   Spring Tides – have the greatest tidal range
    due to the alignment of the Earth-moon-sun
    system (new and full moons)
•   Neap Tides – daily tidal range is less due to
    the sun and moon acting against each other
Spring Tides
Neap Tides
Tidal Patterns
• Tides at various locations respond differently to
    the tide-producing forces
•   Three main tidal patterns exist worldwide:
    diurnal tides, semidiurnal tides, and mixed tides
•   Diurnal Tidal Pattern – characterized by a single
    high tide and a single low tide each tidal day
•   Semidiurnal Tidal Pattern – characterized by two
    high tides and two low tides each tidal day
•   Mixed Tidal Pattern – characterized by a large
    inequality in high water heights, low water
    heights, or both
Tidal Patterns

• Read Chapter 16, Section 2 (pg. 455-460)
• Do Section 16.2 Assessment #1-7 (pg. 460)

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