# Waves and Tides (PowerPoint)

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```					Waves and Tides
Chapter 16, Section 2
Waves

• Ocean waves are energy traveling along
the boundary between ocean and
atmosphere
• 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
Waves
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
basins
•   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
behavior
•   As a wave advances on the shore, the slightly
faster waves further out will catch-up and
decrease the wavelength, making the wave
•   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
BREAK!
Tides
• 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
moon
•   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
tides
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
Assignment

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

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 views: 60 posted: 12/27/2011 language: simple pages: 19